The stack shows 1070 repeated frames of:

• StructElementObject.ProcessChildPrimitive(...)
• StructElementObject.CopyPropertiesTo(...)

The StructureTree import is traversing a cyclic StructElement graph (or equivalent re-entrant child chain) without a recursion guard.

During this recursion, indirect object resolution repeatedly re-enters the same compressed object:

• reference.ObjectNumber = 554
• context.CurrentIndirectReference.ObjectNumber = 554
• TryGetIndirectObject(554, ...) == false at re-entry

PdfStreamWriter: Duplicated pages when merging documents with identical page content streams but different per-page Resources.

Workaround: Use the RadFixedDocument.Merge() method instead of the PdfStreamWriter.

Here is a sample structure of the signature: 

/Type /Sig
/SubFilter /adbe.x509.rsa_sha1
/Filter /Adobe.PPKMS

NetStandard: Missing content due to empty glyph outlines in embedded TrueType font subsets.

Workaround 1

Fully embed the fonts in the result PDF document:

PdfFormatProvider pdfFormatProvider = new PdfFormatProvider();
pdfFormatProvider.ExportSettings.FontEmbeddingType = FontEmbeddingType.Full;

Workaround 2

Switch to a .NET Framework project environment and use the .NET Framework PdfProcessing packages.

PdfStreamWriter stream-copy page splitting performance is much slower than expected in some cases. When working with larger PDF files, the processing time can increase a lot and cause noticeable delays.