When a document containing a SignatureField is exported with the IsEncrypted property set to true, a not set UserPassword is required to open it, which makes it impossible to be opened. An InvalidOperationException is thrown with the message "Password is not correct." when importing with PdfProcessing; Adobe Acrobat also doesn't recognize the password.

Workaround: Exporting with AES256 encryption does not have this problem:

provider.ExportSettings = new PdfExportSettings
{
	IsEncrypted = true,
	EncryptionType = EncryptionType.AES256
};

• Coons patch meshes (type 6) construct a shading from one or more color
  patches, each bounded by four cubic Bézier curves.

When using Telerik Document Processing (PdfProcessing) for embedding Factur-X invoices, the produced PDF document is Non‑compliant with PDF-AF / Factur‑X according to the following validator: 

https://www.superpdp.tech/outils/validateur-facture-electronique/ 

Implement the Exponential Interpolation Function in PdfProcessing. Currently, NotSupportedFunctionTypeException is thrown with a message "Function type 2 is not supported."

After merging several PDF documents, some pages are blank indicating the following error:

With the current implementation when exporting a Stitching function all the containing functions are exported as Sampled functions even if they originally have been imported as Exponential interpolation functions, which leads to an increase in the size of the document.

More information can be found in the PDF Specification.

https://loc.gov/preservation/digital/formats/fdd/fdd000532.shtml

PDF/A‑4f is a version of PDF/A designed for archival storage that:

• Ensures long‑term visual and structural preservation
• Is based on modern PDF 2.0
• Allows embedded files (attachments) that are also archival‑compliant