WPF allows running multiple UI threads in a single process. When RadPdfViewer is used in such scenarios, sometimes InvalidOperationException: 'The calling thread cannot access this object because a different thread owns it.' is thrown. 

Scenarios:
- Show Find dialog (or any other of the dialogs available for register in ExtensibilityManager class) for the first instance, the for the second instance.

• Create new WPFApplication.
• Add a RadPdfViewer to the main window

• Open the pdf file

Text characters are missing when document is loaded in RadPdfViewer. When Fit to Page is used then numerous text characters vanish. They do not reappear when zooming back in.

When loading documents with CFF (Compact Font Format) font source containing .notdef glyph, System.ArgumentException: 'An item with the same key has already been added.', is thrown.

The widgets of the interactive forms are not respected when creating a thumbnail from a PDF page. Implement logic for adding the form fields widgets to the generated image as well.

I want to draw the signature box, like in Adobe Acrobat Reader.

This is very important when the document needs more than 1 signature.

When the FixedDocumentSinglePagePresenter content control is used to visualize PDF files in custom PDF viewer implementation a raise condition can be occurred leading to NullReferenceException with the following stack trace:
at Telerik.Windows.Documents.Fixed.UI.UIElementsHelper.FillPageContentElementsInPanel(Canvas container, RadFixedPage page)
at Telerik.Windows.Documents.UI.FixedDocumentSinglePagePresenter.CreateContent(RadFixedPage page)
at Telerik.Windows.Documents.UI.FixedDocumentSinglePagePresenter.PageLoader_WorkCompleted(Object sender, WorkCompletedEventArgs e)
at Telerik.Windows.Documents.Utilities.ResourceLoader.OnWorkCompleted(WorkCompletedEventArgs args)
at Telerik.Windows.Documents.Utilities.ResourceLoader.Worker_RunWorkerCompleted(Object sender, RunWorkerCompletedEventArgs e)
at System.ComponentModel.BackgroundWorker.OnRunWorkerCompleted(RunWorkerCompletedEventArgs e)
at System.ComponentModel.BackgroundWorker.AsyncOperationCompleted(Object arg)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)

The exception is thrown since the current page is unloaded while the content is being parsed.

The EI keyword defines an operator for ending the image data. When the stream contains the same sequence, the parser treats that as an end of the image data. As a result, the image and the following content cannot be properly parsed and there is missing content when the document is visualized.

By specification, the InteractiveForm fields can have the same name if they are descendants of a common ancestor. Such fields are different representations of the same underlying field; they should differ only in properties that specify their visual appearance. When such a document is imported an ArgumentException: 'An item with the same key has already been added.' is thrown, which leads to non-editable fields in RadPdfViewer.

The CIDFont dictionary may contain an array, describing the widths of the glyphs. If the width has a negative value an ArgumentException: 'Width and Height must be non-negative.', is thrown when the document is imported in RadPdfViewer, which leads to application crash.

The character is visualized as '3'. The same issue is also reproducible when the content is copied from Adobe.

WPF controls are used to visualize the form fields in PdfViewer. However, these controls inherit the background defined in the PdfViewer's theme instead of a background of the form field control. This leads to wrong visualization mostly in the dark themes as the content inside the form field might get unreadable.

There is an exception when the destination is pointing to a page array. This should be handled so the document is displayed. 

Document with invalid cross-reference stream is not loaded correctly

To reproduce:

- Search for a specific word until the last occurrence is found and a message appears. 

- Click the FindPrevious button

Result: A message appears.

Expected: The previous entry is selected. 

The stroke is not rendered when the text is in XForm

Add support for respecting Custom UI Layers when exporting Fixed Page to an image.

When importing document with text containing char code mapped to .notdef glyph name an ArgumentException: 'The encoding is not supported.' is thrown.

When rendering a PDF document page in FixedDocumentSinglePagePresenter, blank pages are displayed, when the document contains images.

Using Adobe the edit mode is triggered on the first mouse click.