diff --git a/Pdf4QtLibCore/sources/pdfannotation.cpp b/Pdf4QtLibCore/sources/pdfannotation.cpp
index 8034779..0cfb66f 100644
--- a/Pdf4QtLibCore/sources/pdfannotation.cpp
+++ b/Pdf4QtLibCore/sources/pdfannotation.cpp
@@ -924,6 +924,11 @@ PDFAnnotationPtr PDFAnnotation::parse(const PDFObjectStorage* storage, PDFObject
         annotation->m_content = PDFRichMediaContent::parse(storage, dictionary->get("RichMediaContent"));
         annotation->m_settings = PDFRichMediaSettings::parse(storage, dictionary->get("RichMediaSettings"));
     }
+    else
+    {
+        // Fill unknown annotation
+        result.reset(new PDFUnknownAnnotation());
+    }
 
     if (!result)
     {
diff --git a/Pdf4QtLibCore/sources/pdfannotation.h b/Pdf4QtLibCore/sources/pdfannotation.h
index 8e58568..1391089 100644
--- a/Pdf4QtLibCore/sources/pdfannotation.h
+++ b/Pdf4QtLibCore/sources/pdfannotation.h
@@ -84,7 +84,8 @@ enum class AnnotationType
     Redact,
     Projection,
     _3D,
-    RichMedia
+    RichMedia,
+    Unknown
 };
 
 enum class AnnotationLineEnding
@@ -1317,6 +1318,15 @@ public:
     virtual AnnotationType getType() const override { return AnnotationType::TrapNet; }
 };
 
+/// Unknown (not recognized) annotation.
+class PDFUnknownAnnotation : public PDFAnnotation
+{
+public:
+    inline explicit PDFUnknownAnnotation() = default;
+
+    virtual AnnotationType getType() const override { return AnnotationType::Unknown; }
+};
+
 /// Watermark annotation represents watermark displayed on the page,
 /// for example, if it is printed. Watermarks are displayed at fixed
 /// position and size on the page.
diff --git a/RELEASES.txt b/RELEASES.txt
index 2f53ea5..a4e1d4f 100644
--- a/RELEASES.txt
+++ b/RELEASES.txt
@@ -1,4 +1,5 @@
 CURRENT:
+ - Issue #168: When opening a PDF file or merging some PDF files, stamp will disappear.
  - Issue #164: Taskbar icon not shown in linux mint.
  - Issue #163: Unable to render probably valid PDF
  - Issue #161: Can it be possible to trust a certificate like in acrobat?