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;

When using CTRL+Mousewheel to zoom in to a PDFViewer document, it should zoom into the point where the mouse pointer is located. Currently it just does a simple zoom of the whole document.

For example see Acrobat Reader or Google Maps.

Due to excessive memory consumption when decoding images, OutOfMemoryException can be thrown when viewing documents with large images inside them. 

Workarounds: 
- Set ExtensibilityManager.MaxImageSize = null. This will skip one resizing step, and could be beneficial in documents containing few large images.
- Use 64-bit process for the client application. This allows the process to consume much more memory. Note that starting 64-bit process while debugging can be tricky, as described in this blog post: https://weblog.west-wind.com/posts/2016/Dec/19/Visual-Studio-Debugging-and-64-Bit-NET-Applications.

Available in R1 2018 Official release version.

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).

Dialog for inputting the password should be implemented in order to be able to decrypt the file content.

When an image is actually consisting of sequence of smaller images, sometimes white lines appear between the smaller images.