Observed when loading a document: 

A rectangle is rendered as a solid rectangle instead of a rectangle with no fill.

It is actually checked and only the appearance is wrong. When the file is saved the checkboxes states are as expected.

This behavior is observed with PdfImportSettings.ReadOnDemand setting only.

While all the pages and components of the control are rendered on the image, the content is completely missing from it. The issue is a regression caused by the migration of the model and its async rendering introduced in R3 2020.

Workaround: Fallback to the old rendering engine:

• Changing the default behavior:

 this.pdfViewer.DefaultImportSettings.UseOldRendering = true;

• Setting the property to the format provider used to show the document:

PdfImportSettings settings = PdfImportSettings.ReadOnDemand;
settings.UseOldRendering = true;

The rendering of the image is not fully parsed and the next attribute cannot be properly read. 

System.InvalidCastException: 'Unable to cast object of type 'Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.PdfArray' to type 'Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.PdfInt'.'

When importing a document with a missing state separator (e.g. linefeed) in the object stream (ObjStm) an exception is thrown: System.InvalidCastException: 'Unable to cast object of type 'Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.PdfDictionary' to type 'Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.PdfInt'.'

А possible workaround could be handling the exceptions: Handling Exceptions.

When the first symbol in the text string array is empty the text translation is not taken into account.

/f-0-1 1 Tf
[<>-3775<0006>15<000700080002>15<0009>]TJ

This leads to a letter misplacement (too far from each other or overlapping each other).