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Improve struct tree splitting docs

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John Whitington 2024-07-22 13:19:48 +01:00
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2 changed files with 29 additions and 9 deletions
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cpdfmanual.pdf
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cpdfmanual.tex
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@ -5176,10 +5176,10 @@ If the drawing range is a single page, and the next page already exists, the dra
\noindent\verb!cpdf -print-struct-tree in.pdf!
\vspace{1.5mm}
\noindent\verb!cpdf -extract-struct-tree in.pdf -o out.json]!
\noindent\verb!cpdf -extract-struct-tree in.pdf -o out.json!
\vspace{1.5mm}
\noindent\verb!cpdf -replace-struct-tree in.json in.pdf -o out.pdf]!
\noindent\verb!cpdf -replace-struct-tree in.json in.pdf -o out.pdf!
\vspace{1.5mm}
\noindent\verb!cpdf -verify "PDF/UA-1(matterhorn)" [-json] in.pdf!
@ -5195,15 +5195,19 @@ If the drawing range is a single page, and the next page already exists, the dra
\end{framed}}
PDF/UA (Universal Accessibility) is a PDF subformat whose rules consist of a set of machine-checkable and human-checkable-only requirements to make PDF documents accessible for all users - for example, those using screen readers. Cpdf has some basic facilities for manipulating the extra PDF constructs which are used in (amongst others) PDF/UA, and a basic verifier for most of the machine-checkable requirements.
PDF/UA (Universal Accessibility) is a PDF subformat whose rules consist of a set of machine-checkable and human-checkable-only requirements to make PDF documents accessible for all users - for example, those using screen readers. Cpdf has some basic facilities for manipulating the extra PDF constructs which are used in (amongst others) PDF/UA, and a basic verifier for many of the machine-checkable requirements.
\section{Structure trees}
In a PDF document, the optional Structure Tree is a parallel construct which describes the logical structure of a document (as opposed to the information for rendering the document on the screen or printing it out, which every PDF of course contains).
In a PDF document, the optional Structure Tree is a parallel construct which describes the logical structure of a document (as opposed to the information for rendering the document on the screen or printing it out, which every PDF of course contains.)
We can print an abbreviated form of the structure tree to standard output with \texttt{cpdf -print-struct-tree in.pdf}:
We can print an abbreviated form of the structure tree to standard output:
\smallgap
\begin{framed}
\noindent\small\verb!cpdf -print-struct-tree in.pdf!
\end{framed}
\noindent This might yield:
\begin{minipage}{\linewidth}
\begin{framed}
@ -5230,7 +5234,13 @@ We can print an abbreviated form of the structure tree to standard output with \
\end{minipage}
\smallgap
\noindent The numbers in parentheses are the page numbers for structure elements, where present. To extract the full structure tree to JSON, we can use \texttt{cpdf -extract-struct-tree in.pdf -o out.json}:
\noindent The numbers in parentheses are the page numbers for structure elements, where present. We can extract the full structure tree to JSON for inspection or manupulation:
\begin{framed}
\noindent\small\verb!cpdf -extract-struct-tree in.pdf -o out.json!
\end{framed}
\noindent Here is a typical fragment:
{\small\begin{verbatim}
[
@ -5272,9 +5282,19 @@ We can print an abbreviated form of the structure tree to standard output with \
\noindent This JSON file contains the structure tree objects from the file, using the format described in chapter \ref{chap:15}. There is a special entry in object \texttt{0} which gives the key to the page object numbers. In this example, there is one page with object number \texttt{52}.
This JSON file can be edited, for example to change text strings, and reapplied with \texttt{cpdf -replace-struct-tree out.json in.pdf -o out.pdf}. If extra objects are required, they should be introduced with negative object numbers: cpdf will renumber them on import so as not to clash with any existing numbers.
This JSON file can be edited, for example to change text strings, and reapplied to the same file from which it was extracted:
To remove a structure tree from a PDF, we can use \texttt{-remove-dict-entry} from Chapter \ref{chap:misc} i.e \texttt{cpdf -remove-dict-entry /StructTreeRoot in.pdf -o out.pdf}.
\begin{framed}
\noindent\small\verb!cpdf -replace-struct-tree out.json in.pdf -o out.pdf!
\end{framed}
\noindent If extra objects are required, they should be introduced with negative object numbers: cpdf will renumber them on import so as not to clash with any existing numbers.
To remove a structure tree from a PDF, we can use \texttt{-remove-dict-entry} from Chapter \ref{chap:misc}, in other words:
\begin{framed}
\noindent\small\verb!cpdf -remove-dict-entry /StructTreeRoot in.pdf -o out.pdf!
\end{framed}
\section{Verifying conformance to PDF/UA}