This exception seems to be related to AES algorithm PaddingMode property. 

Implement ShadingType 7

Wrong text appearance when editing field because of the wrong FieldFlag ("Ff") exported.

Export should take into account JavaScript and produce PDF similar to the original page.

The image stream is not compressed resulting in a bigger size of the generated file.

Images are decompressed during import/export which result in significantly larger files

The current implementation relies on valid cross-reference offsets in the PDF documents so that PDF objects are easily found and parsed. However, a mechanism for importing documents with invalid offsets for the objects inside the stream can be implemented.

CryptographicException is thrown when saving with PdfStreamWriter or importing with PdfFormatProvider.

The exception: System.Security.Cryptography.CryptographicException: 'The input data is not a complete block.'

The current implementation relies on valid cross-reference offsets in the PDF documents so that PDF objects are easily found and parsed. However, we may implement a mechanism for importing documents with invalid offsets for the objects inside the table.

Add a setting that allows enabling printing of protected documents.

Exception when publishing with ReadyToRun option and manually registering fonts.

Missing content when converting a specific PDF to images (mostly text and shapes).

Provide a consistent API for cloning document elements. Currently, we have a public API for cloning documents but not their elements. 

Currently, when users need to add content to an existing page that is rotated, they should manually calculate the positions of the new content if they need to align it with the appearance of the page. Add API allowing them to easily transform the position respecting the top left edge of the page after its rotation.

According to the PDF Specification: The definition of an indirect object in a PDF file consists of its object number and generation number, followed by the value of the object bracketed between the keywords obj and endobj. For example, the definition:
An invalid case:

ArgumentException when the font box contains negative width or height 

When importing documents with more than one cross-reference table that have not Prev tables specified the incorrect table is processed.

After signing a document using the PdfProcessing library and the document is loaded in Adobe Acrobat an error is shown when the signature widget is clicked:
Error during signature verification.  

Adobe Acrobat error.
Expected a dict object.

Wrong matrix calculations lead to incorrect image (Form XObject) during export

The images inside form sources are not correctly positioned and might be invisible.

This issue is regression it works with R2 2020.