Error message: 

Unable to cast object of type 'Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.PdfInt' to type 'Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.MarkedContents.StructAttributeObject'.

InvalidCastException is thrown when importing a document with a structure element with an indirect reference to an integer value.

InvalidCastException: 'Unable to cast object of type 'Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.PdfInt' to type 'Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.MarkedContents.StructElementObject'.'

When you register a font in an ASP.Core project and in a static constructor, the generated PDF document will have this font only the first time you load the web page. Refreshing the page will generate the PDF document but the fonts will be lost.

Note: This worked in the previous version  2025.2.701.

Part of the stack trace: 

System.OutOfMemoryException: Insufficient memory to continue the execution of the program.
   at System.Text.StringBuilder.ExpandByABlock(Int32 minBlockCharCount)
   at System.Text.StringBuilder.AppendWithExpansion(Char value)
   at System.Text.StringBuilder.Append(Char value)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Utilities.CrossReferenceCollectionReader.GetAllText(Reader reader, Int64 minOffset, Int64 maxOffset)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Utilities.CrossReferenceCollectionReader.FindAllObjectOffsets(Reader reader, Dictionary`2 tokenToOffsets, Int64 minOffset, Int64 maxOffset)

Solution - use the ExpandableMemoryStream for the import instead.

PDF content:

Exported text content:

The current implementation of IDisposable implements a simple Dispose method which releases the inner stream resource. However, if the PdfStreamWriter instance is not disposed explicitly by calling Dispose() or by surrounding it in "using" clause, then the inner Stream resource is not Disposed as well. The same applies for PdfFileSource class.

We should implement the IDisposable pattern in a way that the GC disposes the inner stream if needed when collecting the PdfStreamWriter/PdfFileSource class instances.

Corrupted document when exporting "Courier New" subset.

Workaround - fully embed the font:

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

NOTE: There are reports for other fonts' subset, e.g. "ZapfDingbats" font.

The hierarchical document structure is a means to describe the PDF document structure, which is currently not supported. See 10.6.1 Structure Hierarchy on 856 page of the PDF specification for details.
This document structure is an alternative to the standard PDF structure and most non-Adobe software does not support it.

The document might have been created with Adobe software like Adobe LiveCycle Designer. Very often the document contains some fallback text in the standard PDF structure like:
"Please wait... If this message is not eventually replaced by the proper contents of the document, your PDF viewer may not be able to display this type of document."
"The document you are trying to load requires Adobe Reader 8 or higher. You may not have the Adobe Reader installed or your viewing environment may not be properly configured to use Adobe Reader. For information on how to install Adobe Reader and configure your viewing environment please see  http://www.adobe.com/go/pdf_forms_configure."
"For the best experience, open this PDF portfolio in Acrobat X, Reader X, or later."