Provide support for inserting transparent images in Net Standard

Adding a table with the same code leads to different results 

When adding 10 identical tables onе or more have missing rows at the bottom. The seems to be caused by the text measurement. 

Some operators cannot be correctly parsed which causes incomplete import/export

Add support for documents containing RTL (right-to-left) text.

When exporting TextBoxField with a Simple font and a Differences array defined in the Encoding, the CharCodes covered by this array are incorrectly mapped to glyph indices.

When a TrueType font is defined, the mapping of character codes to glyph indices depends on the built-in cmap table mappings defined in the font and the Encoding property defined in the PDF dictionary.

However, the current implementation maps all characters with cmap tables for Microsoft Symbolic and Macintosh Roman, which causes incorrect mapping results, e.g. space characters are mapped to an Ê glyph.

The issue is also described in the following public item: TryGetCharCode for OpenTypeFont uses wrong cmap and returns wrong charcode.

Workaround: Change the font  of the TextBoxField's widget appearance:
foreach (var widget in field.Widgets)
{
    widget.TextProperties.Font = FontsRepository.Helvetica;
}

There are many instances of the internal Transition, State and ImageXObject classes.

This API should provide a method for removing all fields and widgets in the document and draw the default widget appearance in place of the removed widgets.

WORKAROUND: Sample implementation for flattening form fields may be seen in the FlattenFormFields method from the attached demo project.

Currently, RadFixedDocumentInfo is used only for the export of Author, Title, and Description document metadata properties.

I have read that there limitations to PDF files being imported, however, the file being imported  was generated with FixedContentEditor, so, should be able to import?

  using (Stream stream = Stream)
        {
          try
          {
            this._document = provider.Import(stream);
            _InputPath = fileName;
          }
          catch (Exception e)
          {
            Errors = "Could not open file " + fileName + ": " + e.Message;
            this._document = null;
          }
        }
      }

Currently, this missing functionality may be workaround by either drawing the headers and footers with FixedContentEditor or by using RadWordsProcessing PDF export.

Provide an API for externally signing the document hash.

The PDF model allows actions to be defined for widgets using the optional /A entry. 

Implement GetColor method for Indexed color space

Add support for Lab color space to allow clients to import and export documents with Lab color space.

The document text is overlapped and not possible to read for a specific document. Most of the text is moved to the bottom of the page.

It will be possible to add an SVG element in a RadFixedPage so that it can be exported to PDF via the RadPdfProcessing library.

Type 3 fonts are currently not supported.

When exporting a document referencing PdfProcessing`s .NET Standard assemblies with PdfComplianceLevel set an exception is thrown.

The common annotation properties are described in table "Entries common to all annotation dictionaries" of the Pdf specification.

Declined: Handling a partial annotation import-export could lead to exporting invalid PDF documents.