In principle, the blend function B (Cb , Cs ) is used in the compositing formula to customize the blending operation in Adobe transparency imaging model. The blending mode may define any function which yields another result color from the backdrop and source colors. This will allow overlaying objects on each other forming a transparency stack.

Support for the Blend Mode parameter of the external graphic state should be implemented.

When the content of a page is rotated, each glyph is exported on a new line.

Sometimes customers need to create documents using the CMYK colors to meet specific requirements for printing. Expose such functionality in PdfProcessing.

Importing document containing TextBox widgets with NormalContentSource defining text properties, such as FontSize and Position, are exported with incorrect appearance when the value of the field is modified.

Currently adding an Image content element with ImageSource instantiated with a PNG file format leads to NotSupportedException: 'Can not export other than Jpeg and Jpeg2000 and ImageQuality different than High', when exporting the document.

Support for adding PNG images and exporting to PDF should be implemented for PdfProcessing for .NET Standard scenario.

Support for exporting WMF (Windows Metafile) and EMF (Enhanced Metafile) images should be implemented.

Workaround: Convert the WMF images to PNG before exporting:

By the PDF format specification, CIDToGIDMap is optional. The default value is Identity. However when exporting CID Font with missing CIDToGIDMap property the analyzing tool causes the following warning message:

"PDF/A requires that a Type 2 CIDFont has a stream mapping from CIDs to glyph indices or the name Identity as its value."

When merging files the documents might have the same fonts embedded. Then the PdfProcessing should use only one of the fonts and skip embedding the second font in the resulting document.

Documents can be signed using the end certificate of a certificate chain, instead of the whole chain. This improves the performance of the signing.

When there is long text that is out of the used cell range area, this text should be included in page splitting calculations.

Also, when a cell has text that overflows its width, the text is again clipped by the cell boundaries and is not visible in the exported PDF. In a similar case Excel exports the surrounding cells to ensure that the content is visible.

Workaround: Extend the used cell range to include all the cells which the text content spans.

Some documents result in glyphs with wrong widths after import-export. Widths are mixed making some of them to overlap and others to have bigger distance.

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.

Allow the customers to insert DWG files in the PDF documents.

By specification, the InteractiveForm fields can have the same name if they are descendants of a common ancestor. Such fields are different representations of the same underlying field; they should differ only in properties that specify their visual appearance. When such a document is imported an ArgumentException: 'An item with the same key has already been added.' is thrown.

When importing color space defined as an external resource name, a NotSupportedColorSpaceException: 'CS0 color space is not supported.' is thrown.

For example, importing URI Action with invalid mailto URL scheme - mailto:***@***.**(E-mail), throws UriFormatException: 'Invalid URI: The hostname could not be parsed.'

Line annotation displays a single straight line on the page. When opened, it displays a pop-up window containing the text of the associated note.

A free text annotation displays text directly on the page. Unlike an ordinary text annotation, a free text annotation has no open or closed state; instead of being displayed in a pop-up window, the text is always visible.

By specification, the document AcroForm contains fields with no parents. However, some documents may have child fields in the AcroForm. This leads to ArgumentException when importing the child and parent fields - 'An item with the same key has already been added.' since the child field is added twice.

RadPdfProcessing cannot find startxref keyword at the end of a document if the document contains many zero bytes at its end. NotSupportedException is thrown with "Startxref keyword cannot be found" message. 
Workaround: Trim the ending zero bytes before loading the document to PdfProcessing. Example showing this approach can be found in the following KB article:
http://www.telerik.com/support/kb/winforms/details/notsupportedexception-startxref-keyword-cannot-be-found-when-loading-pdf-file-in-radpdfviewer-for-winforms