diff --git a/Pdf4QtLib/Pdf4QtLib.pro b/Pdf4QtLib/Pdf4QtLib.pro
index cceb1c9..b52892b 100644
--- a/Pdf4QtLib/Pdf4QtLib.pro
+++ b/Pdf4QtLib/Pdf4QtLib.pro
@@ -50,6 +50,7 @@ SOURCES += \
     sources/pdfcms.cpp \
     sources/pdfcompiler.cpp \
     sources/pdfdocumentbuilder.cpp \
+    sources/pdfdocumentmanipulator.cpp \
     sources/pdfdocumenttextflow.cpp \
     sources/pdfdocumentwriter.cpp \
     sources/pdfexecutionpolicy.cpp \
@@ -114,6 +115,7 @@ HEADERS += \
     sources/pdfcompiler.h \
     sources/pdfdocumentbuilder.h \
     sources/pdfdocumentdrawinterface.h \
+    sources/pdfdocumentmanipulator.h \
     sources/pdfdocumenttextflow.h \
     sources/pdfdocumentwriter.h \
     sources/pdfexecutionpolicy.h \
diff --git a/Pdf4QtLib/sources/pdfdocument.h b/Pdf4QtLib/sources/pdfdocument.h
index 4572c5a..8a58c8b 100644
--- a/Pdf4QtLib/sources/pdfdocument.h
+++ b/Pdf4QtLib/sources/pdfdocument.h
@@ -15,7 +15,6 @@
 //    You should have received a copy of the GNU Lesser General Public License
 //    along with Pdf4Qt.  If not, see <https://www.gnu.org/licenses/>.
 
-
 #ifndef PDFDOCUMENT_H
 #define PDFDOCUMENT_H
 
diff --git a/Pdf4QtLib/sources/pdfdocumentbuilder.cpp b/Pdf4QtLib/sources/pdfdocumentbuilder.cpp
index cf97287..ecbcc6e 100644
--- a/Pdf4QtLib/sources/pdfdocumentbuilder.cpp
+++ b/Pdf4QtLib/sources/pdfdocumentbuilder.cpp
@@ -679,6 +679,12 @@ void PDFDocumentBuilder::createDocument()
     m_storage.setSecurityHandler(PDFSecurityHandlerPointer(new PDFNoneSecurityHandler()));
 }
 
+void PDFDocumentBuilder::setDocument(const PDFDocument* document)
+{
+    m_storage = document->getStorage();
+    m_version = document->getInfo()->version;
+}
+
 PDFDocument PDFDocumentBuilder::build()
 {
     updateTrailerDictionary(m_storage.getObjects().size());
diff --git a/Pdf4QtLib/sources/pdfdocumentbuilder.h b/Pdf4QtLib/sources/pdfdocumentbuilder.h
index 7543ade..c5e599a 100644
--- a/Pdf4QtLib/sources/pdfdocumentbuilder.h
+++ b/Pdf4QtLib/sources/pdfdocumentbuilder.h
@@ -305,6 +305,10 @@ public:
     /// is edited at call of this function, then it is lost.
     void createDocument();
 
+    /// Sets a document to this builder. If some document
+    /// is edited at call of this function, then it is lost.
+    void setDocument(const PDFDocument* document);
+
     /// Builds a new document. This function can throw exceptions,
     /// if document being built was invalid.
     PDFDocument build();
diff --git a/Pdf4QtLib/sources/pdfdocumentmanipulator.cpp b/Pdf4QtLib/sources/pdfdocumentmanipulator.cpp
new file mode 100644
index 0000000..ae4cc3e
--- /dev/null
+++ b/Pdf4QtLib/sources/pdfdocumentmanipulator.cpp
@@ -0,0 +1,447 @@
+//    Copyright (C) 2021 Jakub Melka
+//
+//    This file is part of Pdf4Qt.
+//
+//    Pdf4Qt is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Lesser General Public License as published by
+//    the Free Software Foundation, either version 3 of the License, or
+//    with the written consent of the copyright owner, any later version.
+//
+//    Pdf4Qt is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Lesser General Public License for more details.
+//
+//    You should have received a copy of the GNU Lesser General Public License
+//    along with Pdf4Qt.  If not, see <https://www.gnu.org/licenses/>.
+
+#include "pdfdocumentmanipulator.h"
+#include "pdfdocumentbuilder.h"
+#include "pdfoptimizer.h"
+
+namespace pdf
+{
+
+PDFOperationResult PDFDocumentManipulator::assemble(const AssembledPages& pages)
+{
+    if (pages.empty())
+    {
+        return tr("Empty page list.");
+    }
+
+    try
+    {
+        classify(pages);
+
+        pdf::PDFDocumentBuilder documentBuilder;
+        if (m_flags.testFlag(SingleDocument))
+        {
+            PDFInteger documentIndex = -1;
+
+            for (const AssembledPage& assembledPage : pages)
+            {
+                if (assembledPage.isDocumentPage())
+                {
+                    documentIndex = assembledPage.documentIndex;
+                }
+            }
+
+            if (documentIndex == -1 || !m_documents.count(documentIndex))
+            {
+                throw PDFException(tr("Invalid document."));
+            }
+
+            documentBuilder.setDocument(m_documents.at(documentIndex));
+        }
+        else
+        {
+            documentBuilder.createDocument();
+        }
+
+        initializeMergedObjects(documentBuilder);
+
+        ProcessedPages processedPages = processPages(documentBuilder, pages);
+        std::vector<PDFObjectReference> adjustedPages;
+        std::transform(processedPages.cbegin(), processedPages.cend(), std::back_inserter(adjustedPages), [](const auto& page) { return page.targetPageReference; });
+        documentBuilder.setPages(adjustedPages);
+
+        // Correct page tree (invalid parents are present)
+        documentBuilder.flattenPageTree();
+        if (!m_flags.testFlag(SingleDocument) || m_flags.testFlag(RemovedPages))
+        {
+            documentBuilder.removeOutline();
+            documentBuilder.removeThreads();
+            documentBuilder.removeDocumentActions();
+            documentBuilder.removeStructureTree();
+        }
+
+        // Jakub Melka: we also create document parts for each document part (if we aren't
+        // manipulating a single document).
+        if (!m_flags.testFlag(SingleDocument))
+        {
+
+            std::vector<size_t> documentPartPageCounts;
+            documentBuilder.createDocumentParts(documentPartPageCounts);
+        }
+
+        pdf::PDFDocument mergedDocument = documentBuilder.build();
+
+        // Optimize document - remove unused objects and shrink object storage
+        finalizeDocument(&mergedDocument);
+    }
+    catch (PDFException exception)
+    {
+        return exception.getMessage();
+    }
+
+    return true;
+}
+
+PDFDocumentManipulator::ProcessedPages PDFDocumentManipulator::processPages(PDFDocumentBuilder& documentBuilder, const AssembledPages& pages)
+{
+    ProcessedPages processedPages;
+
+    // First, decide, if we are manipulating a single document, or
+    // an array of documents. If the former is the case, then we do not
+    // want to copy objects, it is just unnecessary. If the latter is the case,
+    // then we must
+
+    if (m_flags.testFlag(SingleDocument))
+    {
+        documentBuilder.flattenPageTree();
+        std::vector<PDFObjectReference> pageReferences = documentBuilder.getPages();
+        std::set<PDFObjectReference> usedPages;
+
+        processedPages.reserve(pageReferences.size());
+        for (const AssembledPage& assembledPage : pages)
+        {
+            ProcessedPage processedPage;
+            processedPage.assembledPage = assembledPage;
+
+            if (assembledPage.isDocumentPage())
+            {
+                const PDFInteger pageIndex = assembledPage.pageIndex;
+
+                if (pageIndex < 0 || pageIndex >= PDFInteger(pageReferences.size()))
+                {
+                    throw PDFException(tr("Missing page (%1) in a document.").arg(pageIndex));
+                }
+
+                PDFObjectReference pageReference = pageReferences[pageIndex];
+                if (!usedPages.count(pageReference))
+                {
+                    processedPage.targetPageReference = pageReference;
+                    usedPages.insert(pageReference);
+                }
+                else
+                {
+                    // Page is being cloned. So we must clone it...
+                    std::vector<pdf::PDFObjectReference> references = pdf::PDFDocumentBuilder::createReferencesFromObjects(documentBuilder.copyFrom(pdf::PDFDocumentBuilder::createObjectsFromReferences({ pageReference }), *documentBuilder.getStorage(), true));
+                    Q_ASSERT(references.size() == 1);
+                    processedPage.targetPageReference = references.front();
+                    usedPages.insert(references.front());
+                }
+            }
+
+            processedPages.push_back(processedPage);
+        }
+    }
+    else
+    {
+        processedPages = collectObjectsAndCopyPages(documentBuilder, pages);
+    }
+
+    // Now, create "special" pages, such as image pages or blank pages, and rotate
+    // final pages (we must check, that page object exists).
+    for (ProcessedPage& processedPage : processedPages)
+    {
+        if (processedPage.assembledPage.isBlankPage() || processedPage.assembledPage.isImagePage())
+        {
+            QImage image;
+
+            if (processedPage.assembledPage.isImagePage())
+            {
+                const PDFInteger imageIndex = processedPage.assembledPage.imageIndex;
+
+                if (!m_images.count(imageIndex))
+                {
+                    throw PDFException(tr("Missing image."));
+                }
+
+                image = m_images.at(imageIndex);
+
+                if (image.isNull())
+                {
+                    throw PDFException(tr("Missing image."));
+                }
+            }
+
+            QRectF pageRect = QRectF(QPointF(0, 0), processedPage.assembledPage.pageSize * PDF_MM_TO_POINT);
+            processedPage.targetPageReference = documentBuilder.appendPage(pageRect);
+            PDFPageContentStreamBuilder contentStreamBuilder(&documentBuilder);
+
+            QPainter* painter = contentStreamBuilder.begin(processedPage.targetPageReference);
+
+            if (processedPage.assembledPage.isImagePage())
+            {
+                // Just paint the image
+                painter->drawImage(pageRect, image);
+            }
+
+            contentStreamBuilder.end(painter);
+        }
+
+        if (!processedPage.targetPageReference.isValid())
+        {
+            throw PDFException(tr("Error occured during page creation."));
+        }
+
+        documentBuilder.setPageRotation(processedPage.targetPageReference, processedPage.assembledPage.pageRotation);
+    }
+
+    return processedPages;
+}
+
+PDFDocumentManipulator::ProcessedPages PDFDocumentManipulator::collectObjectsAndCopyPages(PDFDocumentBuilder& documentBuilder, const AssembledPages& pages)
+{
+    ProcessedPages processedPages;
+    processedPages.reserve(pages.size());
+
+    std::map<std::pair<int, int>, PDFObjectReference> documentPages;
+
+    for (const AssembledPage& assembledPage : pages)
+    {
+        ProcessedPage processedPage;
+        processedPage.assembledPage = assembledPage;
+        processedPages.push_back(processedPage);
+
+        if (assembledPage.isDocumentPage())
+        {
+            documentPages[std::make_pair(assembledPage.documentIndex, assembledPage.pageIndex)] = PDFObjectReference();
+        }
+    }
+
+    for (auto it = documentPages.begin(); it != documentPages.end();)
+    {
+        const int documentIndex = it->first.first;
+
+        // Jakub Melka: we will find end of a single document page range
+        auto itEnd = it;
+        while (itEnd != documentPages.end() && itEnd->first.first == documentIndex)
+        {
+            ++itEnd;
+        }
+
+        if (documentIndex != -1)
+        {
+            // Check we have the document
+            if (!m_documents.count(documentIndex))
+            {
+                throw PDFException(tr("Invalid document."));
+            }
+            const PDFDocument* document = m_documents.at(documentIndex);
+
+            // Copy the pages into the target document builder
+            std::vector<PDFInteger> pageIndices;
+            for (auto currentIt = it; currentIt != itEnd; ++currentIt)
+            {
+                pageIndices.push_back(currentIt->first.second);
+            }
+
+            pdf::PDFDocumentBuilder temporaryBuilder(document);
+            temporaryBuilder.flattenPageTree();
+
+            std::vector<pdf::PDFObjectReference> currentPages = temporaryBuilder.getPages();
+            std::vector<pdf::PDFObjectReference> objectsToMerge;
+            objectsToMerge.reserve(std::distance(it, itEnd));
+
+            for (int pageIndex : pageIndices)
+            {
+                if (pageIndex < 0 || pageIndex >= currentPages.size())
+                {
+                    throw PDFException(tr("Missing page (%1) in a document.").arg(pageIndex));
+                }
+
+                objectsToMerge.push_back(currentPages[pageIndex]);
+            }
+
+            pdf::PDFObjectReference acroFormReference;
+            pdf::PDFObjectReference namesReference;
+            pdf::PDFObjectReference ocPropertiesReference;
+
+            pdf::PDFObject formObject = document->getCatalog()->getFormObject();
+            if (formObject.isReference())
+            {
+                acroFormReference = formObject.getReference();
+            }
+            else
+            {
+                acroFormReference = temporaryBuilder.addObject(formObject);
+            }
+
+            if (const pdf::PDFDictionary* catalogDictionary = temporaryBuilder.getDictionaryFromObject(temporaryBuilder.getObjectByReference(temporaryBuilder.getCatalogReference())))
+            {
+                pdf::PDFObject namesObject = catalogDictionary->get("Names");
+                if (namesObject.isReference())
+                {
+                    namesReference = namesObject.getReference();
+                }
+
+                pdf::PDFObject ocPropertiesObject = catalogDictionary->get("OCProperties");
+                if (ocPropertiesObject.isReference())
+                {
+                    ocPropertiesReference = ocPropertiesObject.getReference();
+                }
+            }
+
+            if (!namesReference.isValid())
+            {
+                namesReference = temporaryBuilder.addObject(pdf::PDFObject());
+            }
+
+            if (!ocPropertiesReference.isValid())
+            {
+                ocPropertiesReference = temporaryBuilder.addObject(pdf::PDFObject());
+            }
+
+            objectsToMerge.insert(objectsToMerge.end(), { acroFormReference, namesReference, ocPropertiesReference });
+
+            // Now, we are ready to merge objects into target document builder
+            std::vector<pdf::PDFObjectReference> references = pdf::PDFDocumentBuilder::createReferencesFromObjects(documentBuilder.copyFrom(pdf::PDFDocumentBuilder::createObjectsFromReferences(objectsToMerge), *temporaryBuilder.getStorage(), true));
+
+            ocPropertiesReference = references.back();
+            references.pop_back();
+            namesReference = references.back();
+            references.pop_back();
+            acroFormReference = references.back();
+            references.pop_back();
+
+            documentBuilder.appendTo(m_mergedObjects[MOT_OCProperties], documentBuilder.getObjectByReference(ocPropertiesReference));
+            documentBuilder.appendTo(m_mergedObjects[MOT_Form], documentBuilder.getObjectByReference(acroFormReference));
+            documentBuilder.mergeNames(m_mergedObjects[MOT_Names], namesReference);
+
+            Q_ASSERT(references.size() == std::distance(it, itEnd));
+
+            auto referenceIt = references.begin();
+            for (auto currentIt = it; currentIt != itEnd; ++currentIt, ++referenceIt)
+            {
+                it->second = *referenceIt;
+            }
+        }
+
+        // Advance the index
+        it = itEnd;
+    }
+
+    std::set<PDFObjectReference> usedReferences;
+    for (ProcessedPage& processedPage : processedPages)
+    {
+        if (processedPage.assembledPage.isDocumentPage())
+        {
+            auto key = std::make_pair(processedPage.assembledPage.documentIndex, processedPage.assembledPage.pageIndex);
+            Q_ASSERT(documentPages.count(key));
+
+            PDFObjectReference pageReference = documentPages.at(key);
+            if (!usedReferences.count(pageReference))
+            {
+                processedPage.targetPageReference = pageReference;
+                usedReferences.insert(pageReference);
+            }
+            else
+            {
+                // Page is being cloned. So we must clone it...
+                std::vector<pdf::PDFObjectReference> references = pdf::PDFDocumentBuilder::createReferencesFromObjects(documentBuilder.copyFrom(pdf::PDFDocumentBuilder::createObjectsFromReferences({ pageReference }), *documentBuilder.getStorage(), true));
+                Q_ASSERT(references.size() == 1);
+                processedPage.targetPageReference = references.front();
+                usedReferences.insert(references.front());
+            }
+        }
+    }
+
+    return processedPages;
+}
+
+void PDFDocumentManipulator::classify(const AssembledPages& pages)
+{
+    m_flags = None;
+
+    std::set<PDFInteger> documentIndices;
+    std::set<PDFInteger> pageIndices;
+    for (const AssembledPage& assembledPage : pages)
+    {
+        documentIndices.insert(assembledPage.documentIndex);
+        pageIndices.insert(assembledPage.pageIndex);
+    }
+
+    documentIndices.erase(-1);
+    pageIndices.erase(-1);
+
+    m_flags.setFlag(SingleDocument, documentIndices.size() == 1);
+
+    if (m_flags.testFlag(SingleDocument) && m_documents.count(*documentIndices.begin()))
+    {
+        const PDFDocument* document = m_documents.at(*documentIndices.begin());
+        const bool pagesRemoved = pageIndices.size() < document->getCatalog()->getPageCount();
+        m_flags.setFlag(RemovedPages, pagesRemoved);
+    }
+}
+
+void PDFDocumentManipulator::initializeMergedObjects(PDFDocumentBuilder& documentBuilder)
+{
+    m_mergedObjects[MOT_OCProperties] = documentBuilder.addObject(PDFObject());
+    m_mergedObjects[MOT_Form] = documentBuilder.addObject(PDFObject());
+    m_mergedObjects[MOT_Names] = documentBuilder.addObject(PDFObject());
+}
+
+void PDFDocumentManipulator::finalizeMergedObjects(PDFDocumentBuilder& documentBuilder)
+{
+    if (!m_flags.testFlag(SingleDocument))
+    {
+        if (!documentBuilder.getObjectByReference(m_mergedObjects[MOT_OCProperties]).isNull())
+        {
+            documentBuilder.setCatalogOptionalContentProperties(m_mergedObjects[MOT_OCProperties]);
+        }
+
+        if (!documentBuilder.getObjectByReference(m_mergedObjects[MOT_Names]).isNull())
+        {
+            documentBuilder.setCatalogNames(m_mergedObjects[MOT_Names]);
+        }
+
+        if (!documentBuilder.getObjectByReference(m_mergedObjects[MOT_Form]).isNull())
+        {
+            documentBuilder.setCatalogAcroForm(m_mergedObjects[MOT_Form]);
+        }
+    }
+}
+
+void PDFDocumentManipulator::finalizeDocument(PDFDocument* document)
+{
+    auto optimizationFlags = pdf::PDFOptimizer::OptimizationFlags(PDFOptimizer::RemoveUnusedObjects |
+                                                                  PDFOptimizer::ShrinkObjectStorage |
+                                                                  PDFOptimizer::DereferenceSimpleObjects |
+                                                                  PDFOptimizer::MergeIdenticalObjects);
+    PDFOptimizer optimizer(optimizationFlags, nullptr);
+    optimizer.setDocument(document);
+    optimizer.optimize();
+    PDFDocument mergedDocument = optimizer.takeOptimizedDocument();
+
+    // We must adjust some objects - they can have merged objects
+    pdf::PDFDocumentBuilder finalBuilder(&mergedDocument);
+    if (const pdf::PDFDictionary* dictionary = finalBuilder.getDictionaryFromObject(finalBuilder.getObjectByReference(finalBuilder.getCatalogReference())))
+    {
+        pdf::PDFDocumentDataLoaderDecorator loader(finalBuilder.getStorage());
+        pdf::PDFObjectReference ocPropertiesReference = loader.readReferenceFromDictionary(dictionary, "OCProperties");
+        if (ocPropertiesReference.isValid())
+        {
+            finalBuilder.setObject(ocPropertiesReference, pdf::PDFObjectManipulator::removeDuplicitReferencesInArrays(finalBuilder.getObjectByReference(ocPropertiesReference)));
+        }
+        pdf::PDFObjectReference acroFormReference = loader.readReferenceFromDictionary(dictionary, "AcroForm");
+        if (acroFormReference.isValid())
+        {
+            finalBuilder.setObject(acroFormReference, pdf::PDFObjectManipulator::removeDuplicitReferencesInArrays(finalBuilder.getObjectByReference(acroFormReference)));
+        }
+    }
+    m_assembledDocument = finalBuilder.build();
+}
+
+}   // namespace pdf
diff --git a/Pdf4QtLib/sources/pdfdocumentmanipulator.h b/Pdf4QtLib/sources/pdfdocumentmanipulator.h
new file mode 100644
index 0000000..7d844e2
--- /dev/null
+++ b/Pdf4QtLib/sources/pdfdocumentmanipulator.h
@@ -0,0 +1,140 @@
+//    Copyright (C) 2021 Jakub Melka
+//
+//    This file is part of Pdf4Qt.
+//
+//    Pdf4Qt is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Lesser General Public License as published by
+//    the Free Software Foundation, either version 3 of the License, or
+//    with the written consent of the copyright owner, any later version.
+//
+//    Pdf4Qt is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Lesser General Public License for more details.
+//
+//    You should have received a copy of the GNU Lesser General Public License
+//    along with Pdf4Qt.  If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef PDFDOCUMENTMANIPULATOR_H
+#define PDFDOCUMENTMANIPULATOR_H
+
+#include "pdfdocument.h"
+#include "pdfutils.h"
+
+#include <QImage>
+
+namespace pdf
+{
+
+/// Document page assembler/manipulator. Can assemble document(s) pages
+/// to a new document, where pages are inserted/removed/moved, or joined
+/// from another documents, or blank pages/image pages inserted. Document
+/// is also optimized.
+class Pdf4QtLIBSHARED_EXPORT PDFDocumentManipulator
+{
+    Q_DECLARE_TR_FUNCTIONS(pdf::PDFDocumentManipulator)
+
+public:
+    explicit PDFDocumentManipulator() = default;
+
+    struct AssembledPage
+    {
+        PDFInteger documentIndex = -1; ///< Source document index. If page is not from a document, value is -1.
+        PDFInteger imageIndex = -1; ///< Source image index. If page is not from a image, value is -1.
+        PDFInteger pageIndex = -1; ///< Source document page index. If page is not from a document, value is -1.
+        QSizeF pageSize; ///< Unrotated page size
+        PageRotation pageRotation = PageRotation::None; ///< Page rotation
+
+        constexpr bool isDocumentPage() const { return documentIndex != -1; }
+        constexpr bool isImagePage() const { return imageIndex != -1; }
+        constexpr bool isBlankPage() const { return documentIndex == -1 && imageIndex == -1; }
+    };
+
+    using AssembledPages = std::vector<AssembledPage>;
+
+    /// Adds document with given index to available document list
+    /// \param documentIndex Document index
+    /// \param document Document
+    void addDocument(int documentIndex, const PDFDocument* document) { m_documents[documentIndex] = document; }
+
+    /// Adds image with given index to available image list
+    /// \param imageIndex Image index
+    /// \param image Image
+    void addImage(int imageIndex, QImage image) { m_images[imageIndex] = std::move(image); }
+
+    /// Assembles pages into a new document. Returns true, if a new document
+    /// was assembled, otherwise error message is being returned. Assebmled
+    /// document can be accessed trough a given getters.
+    /// \param pages Pages
+    /// \returns True or error message
+    PDFOperationResult assemble(const AssembledPages& pages);
+
+    /// Returns reference to an assembled document. This function should
+    /// be called only, if method \p assemble returns true, otherwise
+    /// undefined document can be returned.
+    /// \returns Assembled document
+    const PDFDocument& getAssembledDocument() const { return m_assembledDocument; }
+
+    /// Returns rvalue reference to an assembled document. This function should
+    /// be called only, if method \p assemble returns true, otherwise
+    /// undefined document can be returned.
+    /// \returns Assembled document
+    PDFDocument&& takeAssembledDocument() { return std::move(m_assembledDocument); }
+
+    static constexpr AssembledPage createDocumentPage(int documentIndex, int pageIndex, QSizeF pageSize, PageRotation pageRotation) { return AssembledPage{ documentIndex, -1, pageIndex, pageSize, pageRotation}; }
+    static constexpr AssembledPage createImagePage(int imageIndex, QSizeF pageSize, PageRotation pageRotation) { return AssembledPage{ -1, imageIndex, -1, pageSize, pageRotation}; }
+    static constexpr AssembledPage createBlankPage(QSizeF pageSize, PageRotation pageRotation) { return AssembledPage{ -1, -1, -1, pageSize, pageRotation}; }
+
+private:
+
+    struct ProcessedPage
+    {
+        AssembledPage assembledPage;
+        PDFObjectReference targetPageReference;
+    };
+
+    using ProcessedPages = std::vector<ProcessedPage>;
+
+    enum AssembleFlag
+    {
+        None            = 0x0000,
+        SingleDocument  = 0x0001, ///< We are assembling a single page document (possibly with blank pages / image pages
+        RemovedPages    = 0x0002, ///< Document contains removed pages
+    };
+    Q_DECLARE_FLAGS(AssembleFlags, AssembleFlag)
+
+    enum MergedObjectType
+    {
+        MOT_OCProperties,
+        MOT_Form,
+        MOT_Names,
+        MOT_Last
+    };
+
+    /// Processes pages given a page list and a document builder.
+    /// \param documentBuilder Document builder
+    /// \param pages Pages to be processed
+    /// \returns Processed pages
+    ProcessedPages processPages(PDFDocumentBuilder& documentBuilder, const AssembledPages& pages);
+
+    /// Collects objects and copies them into the target document builder.
+    /// \param documentBuilder Document builder
+    /// \param pages Pages to be copied
+    /// \returns Processed pages
+    ProcessedPages collectObjectsAndCopyPages(PDFDocumentBuilder& documentBuilder, const AssembledPages& pages);
+
+    void classify(const AssembledPages& pages);
+    void initializeMergedObjects(PDFDocumentBuilder& documentBuilder);
+    void finalizeMergedObjects(PDFDocumentBuilder& documentBuilder);
+    void finalizeDocument(PDFDocument* document);
+
+    std::map<PDFInteger, const PDFDocument*> m_documents;
+    std::map<PDFInteger, QImage> m_images;
+    AssembleFlags m_flags = None;
+    std::array<PDFObjectReference, MOT_Last> m_mergedObjects = { };
+    PDFDocument m_assembledDocument;
+};
+
+}   // namespace pdf
+
+#endif // PDFDOCUMENTMANIPULATOR_H
diff --git a/Pdf4QtLib/sources/pdfglobal.h b/Pdf4QtLib/sources/pdfglobal.h
index e4dafbc..168c74c 100644
--- a/Pdf4QtLib/sources/pdfglobal.h
+++ b/Pdf4QtLib/sources/pdfglobal.h
@@ -120,6 +120,7 @@ struct PDFTranslationContext
 constexpr PDFReal PDF_POINT_TO_INCH = 1.0 / 72.0;
 constexpr PDFReal PDF_INCH_TO_MM = 25.4; // [mm / inch]
 constexpr PDFReal PDF_POINT_TO_MM = PDF_POINT_TO_INCH * PDF_INCH_TO_MM;
+constexpr PDFReal PDF_MM_TO_POINT = 1.0 / PDF_POINT_TO_MM;
 
 /// This is default "DPI", but in milimeters, so the name is DPMM (device pixel per milimeter)
 constexpr PDFReal PDF_DEFAULT_DPMM = 96.0 / PDF_INCH_TO_MM;
@@ -129,6 +130,11 @@ constexpr PDFReal convertPDFPointToMM(PDFReal point)
     return point * PDF_POINT_TO_MM;
 }
 
+constexpr PDFReal convertMMToPDFPoint(PDFReal point)
+{
+    return point * PDF_MM_TO_POINT;
+}
+
 class PDFBoolGuard final
 {
 public:
diff --git a/PdfTool/pdftoolunite.cpp b/PdfTool/pdftoolunite.cpp
index 17aa5a4..d1f19ba 100644
--- a/PdfTool/pdftoolunite.cpp
+++ b/PdfTool/pdftoolunite.cpp
@@ -87,9 +87,9 @@ int PDFToolUnite::execute(const PDFToolOptions& options)
                 return ErrorDocumentReading;
             }
 
-            if (!document.getStorage().getSecurityHandler()->isAllowed(pdf::PDFSecurityHandler::Permission::CopyContent))
+            if (!document.getStorage().getSecurityHandler()->isAllowed(pdf::PDFSecurityHandler::Permission::Assemble))
             {
-                PDFConsole::writeError(PDFToolTranslationContext::tr("Document doesn't allow to copy content."), options.outputCodec);
+                PDFConsole::writeError(PDFToolTranslationContext::tr("Document doesn't allow to assemble pages."), options.outputCodec);
                 return ErrorPermissions;
             }
 
@@ -120,20 +120,12 @@ int PDFToolUnite::execute(const PDFToolOptions& options)
                 {
                     namesReference = namesObject.getReference();
                 }
-                else
-                {
-                    namesReference = temporaryBuilder.addObject(namesObject);
-                }
 
                 pdf::PDFObject ocPropertiesObject = catalogDictionary->get("OCProperties");
                 if (ocPropertiesObject.isReference())
                 {
                     ocPropertiesReference = ocPropertiesObject.getReference();
                 }
-                else
-                {
-                    ocPropertiesReference = temporaryBuilder.addObject(ocPropertiesObject);
-                }
             }
 
             if (!namesReference.isValid())
@@ -148,7 +140,7 @@ int PDFToolUnite::execute(const PDFToolOptions& options)
 
             objectsToMerge.insert(objectsToMerge.end(), { acroFormReference, namesReference, ocPropertiesReference });
 
-            // Now, we are ready to merge objects into targed document builder
+            // Now, we are ready to merge objects into target document builder
             std::vector<pdf::PDFObjectReference> references = pdf::PDFDocumentBuilder::createReferencesFromObjects(documentBuilder.copyFrom(pdf::PDFDocumentBuilder::createObjectsFromReferences(objectsToMerge), *temporaryBuilder.getStorage(), true));
 
             ocPropertiesReference = references.back();