When exporting a document that contains a Widget created with FixedContentEditor an exception is thrown: System.ArgumentNullException: 'Value cannot be null. Parameter name: context'

It can be reproduced using the following code snippet:

RadFixedDocument document = new RadFixedDocument();
var page = document.Pages.AddPage();
FixedContentEditor editor = new FixedContentEditor(page);

PushButtonField pushButton = new PushButtonField("button");
editor.Position.Translate(20, 450);
editor.DrawWidget(pushButton, new Size(100, 20));

string path = "Exported.pdf";
File.Delete(path);

using (Stream output = File.OpenWrite(path))
{
	PdfFormatProvider provider = new PdfFormatProvider();
	provider.Export(document, output);
}

document.AcroForm.FormFields.Add(pushButton);

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'

From the PDF Specification: "An ink annotation represents a freehand “scribble” composed of one or more disjoint paths. When opened, it displays a pop-up window containing the text of the associated note."

Such fonts are:

• ArialMT - should fallback to Arial
• TimesNewRomanPS-ItalicMT, TimesNewRomanPS-BoldMT, TimesNewRomanPS-BoldItalicMT - should fallback to the Times New Roman variants accordingly. 

Cell borders are not set when the border is set on the table:

 <table border="1">

Currently RadFixedDocumentInfo is used only for export of Author, Title and Description document metadata properties. This should be extended to support custom properties. We should also implement the import of RadFixedDocumentInfo.

PDF/A-1a is with conformance level A (for "accessibility"), and must adhere to all of the requirements of the PDF Reference as modified by the ISO 19005 specification. 

It requires structural and semantic properties to be preserved. Level 1a uses “Tagged PDF” and Unicode character maps to preserve the document's logical structure and content text stream in natural reading order. 

The following features are used:
- Language specification
- Hierarchical document structure
- Tagged text spans and descriptive text for images and symbols
- Character mappings to Unicode

The purpose is to improve accessibility and make the content accessible for screen readers.

Currently, for .NET Framework scenarios, this could be achieved using RadPdfViewer's WPF control ThumbnailFactory class. Sample code may be seen at this forum post:
http://www.telerik.com/forums/pdf-thumbnail-returns-transparent-images#jO33X-E8Cki_qLh_KsToWg.
The feature should be implemented for .NET Standard as well.

Provide API or mechanism for reusing the already embedded fonts instead of creating a new one when editing an existing document. 

This causes an issue in adobe preflight (font name is not unique).  

The issue is observed when performing merge with RadFixedDocument as well.