Error splitting PDF with PDFSharp 7 vs 6.2.4 #363

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1. ThomasHoevel

   added

   Cannot Reproducehttps://xkcd.com/583/https://xkcd.com/583/

   on Apr 27, 2026
2. ThomasHoevel commented on Apr 27, 2026

   

   ThomasHoevel

   on Apr 27, 2026

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   Unfortunately we probably won't be able to fix this without a sample PDF.
3. Sebastian-Buitrag0 commented on Aug 22, 2026

   

   Sebastian-Buitrag0

   on Aug 22, 2026

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   I hit what looks like the same underlying issue on the 6.2.x line (not the 7.x preview), and tracked it down to a minimal, fully reproducible case.

   Root cause: PdfCrossReferenceTable.TransitiveClosureImplementation's local FindReferencedItems(PdfObject pdfObj) only sets items when the object is a PdfDictionary or PdfArray:

   IEnumerable? items = null;
   PdfDictionary? dict;
   PdfArray? array;
   if ((dict = pdfObj as PdfDictionary) is not null)
       items = dict.Elements.Values;
   else if ((array = pdfObj as PdfArray) is not null)
       items = array.Elements;
   else
       Debug.Assert(false, "Should not come here.");   // no-op in Release
   
   foreach (PdfItem item in items)   // NullReferenceException when items is still null

   Any indirect object that resolves to something other than a dictionary or array (e.g. a bare PdfIntegerObject) hits this and throws. In my case, the source PDF (produced by pdf-lib) writes each page's /Rotate value as an indirect reference to an integer object instead of inlining it — legal PDF, but not what this code path expects.

   Minimal repro (402 bytes total, no real content — reconstructable byte-for-byte from the object layout below):

   1 0 obj << /Type /Catalog /Pages 2 0 R >> endobj
   2 0 obj << /Type /Pages /Kids [3 0 R] /Count 1 >> endobj
   3 0 obj << /Type /Page /Parent 2 0 R /MediaBox [0 0 200 200] /Rotate 4 0 R /Resources << >> >> endobj
   4 0 obj 0 endobj
   

   i.e. a single page whose /Rotate is 4 0 R, where object 4 is just the integer 0.

   var input = PdfReader.Open(File.OpenRead("minimal_repro.pdf"), PdfDocumentOpenMode.Import);
   var outDoc = new PdfDocument();
   outDoc.AddPage(input.Pages[0]); // throws NullReferenceException on 6.2.0–6.2.4

   Version matrix (same file):

   Version	Result
   6.0.0 / 6.1.0 / 6.1.1	OK
   6.2.0 – 6.2.4	NullReferenceException at FindReferencedItems
   7.0.0-preview-1	different error, same call path (InvalidOperationException: Primitive indirect object of type 'PdfIntegerObject' cannot be transformed to type 'PdfInteger' — so still broken, just fails differently)

   6.1.1 still uses TransitiveClosureImplementation_old, which doesn't hit this code path — that's presumably why the regression window starts at 6.2.0.

   Happy to share the repro file or test a patch if useful.
4. ThomasHoevel commented on Aug 24, 2026

   

   ThomasHoevel

   on Aug 24, 2026

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   Happy to share the repro file or test a patch if useful.

   Thanks for your feedback. Please share the file here. Thanks.
5. ThomasHoevel commented on Aug 25, 2026

   

   ThomasHoevel

   on Aug 25, 2026

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   Happy to share the repro file or test a patch if useful.

   Thanks for your feedback. Please share the file here. Thanks.

   Never mind, we created a test PDF.
6. Sebastian-Buitrag0 commented on Aug 25, 2026

   

   Sebastian-Buitrag0

   on Aug 25, 2026

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   Hi, @ThomasHoevel sorry: I couldn't share the PDF because it contained private information, but I included an explanation of how to recreate it so you can test it out.