Add support for the PAdES-BES signature standard

Add support for /TR (Transfer Function) property of SMask.

ArgumentNullException is thrown when importing a restricted, AES-encrypted document.

Creating a document from an SVG image with a CapPathRound (stroke-linecap="round") adds unexpected lines.

Fields are no longer highlighted after import. 

The issue may be reproduced by opening the attached PDF in Adobe Reader. Although the viewer initially shows the characters correctly, when you start typing in the TextBox, the umlaut/diacritics characters get corrupted. In other PDF viewers, the umlaut characters are handled correctly, so the issue seems to related to concrete Adobe Reader encoding handling implementation. The diacritic characters are handled incorrectly in other viewers as well (e.g. Chrome).

Field border appearance are lost during import-export of the document

When importing a document with an invalid creation or modification date, an exception is thrown:

• FormatException: 'The input string '' was not in a correct format.'
• ArgumentOutOfRangeException: 'Year, Month, and Day parameters describe an unrepresentable DateTime.'

Fields are doubled according to ItextSharp after import/export. 

When a Pdf document contains TextBoxFields some of which are hidden and you merge it with another document, the hidden state is reset and the field appears in the merged document:

Before:

After:

 

KeyNotFoundException is thrown when importing a document with a structure element that references a page that is not part of the page collection.

System.ArgumentException: 'An item with the same key has already been added. Key: Telerik.Windows.Documents.Fixed.Model.InteractiveForms.RadioButtonField'

It is reproducible when you have at least 2 pages with RadioButtonFields. The import operation goes smoothly. However, merging or removing a page after import leads to the described error.

When decoding the image with a CCITTFaxDecode filter an exception is thrown: NullReferenceException: 'Object reference not set to an instance of an object.'

OutOfMemoryException is thrown when importing a large document with invalid cross-reference table.

Multiple graphic state objects are lost on import.

When loading a PDF generated with PdfProcessing in PDF Accessibility Checker 2021 (PAC) an exception is thrown: "Object reference not set to an instance of an object".

It is reproducible with all PdfComplianceLevel export options.

From the Part 4: PAdES Long Term - PAdES-LTV Profile (ETSI TS 102 778-4) Specification: 

"Validation of an electronic signature requires data to validate the signature such as CA certificates, Certificate Revocation List (CRLs) or Certificate status information (OCSP) commonly provided by an online service (referred to in the present document as validation data). If the document is stored and the signatures are to be verifiable long after first created, in particular after the signing certificate has expired, the original validation data may no longer available or there may uncertainty as to what validation data was used when the document was first verified."

When writing a RadFixedPage containing widgets using the PdfPageStreamWriter.WriteContent() method an exception is thrown.

The exception: System.ArgumentNullException: 'Value cannot be null. Parameter name: context'

The appearance of a form field button is lost after import-export.

Provide an API for externally signing the document hash.