RadPdfViewer partially supports CCITTFaxDecode (that is basically TIFF). There are some limitations that are not supported at this stage like EncodedByteAlign = true or Group 3, 2-D encoding.

They are used by the page and the XObjects drawn on it and deal with the overlaying of the colors. These groups are described on page 556 of PdfReference 1.7. 

Add PrintPreview dialog visualizing the way the document is going to be printed.

An implementation of JPXDecoder should be created to allow the decompression of data encoded using the wavelet-based JPEG2000 standard.

Guidelines of how to provide a custom implementation of the JPXDecode filter can be found in the Customize Rendering section of the documentation and a sample implementation can be found in the SDK examples.

Bitonal image scaling algorithms which improve the readability of bitonal, black and white images. Due to the lack of colors within the palette of 1-bit black and white images, they become splotchy and distorted when zoomed in or out

In Adobe and Foxit readers, the user can draw different shapes, which are later saved as images in the document.

Add built-in localization for the UI control and its tooltips. Currently they can be localized by expanding the XAML of RadPdfViewerToolBar and adding the required resources to the code.

Images hosted inside multiple Form XObjects are not rendered.

Currently, RadPdfViewer uses WPF DrawingContext class for drawing page elements to a Canvas.  When PDF page has many content elements (usually geometries) drawing the page may be time-consuming and freezes the UI. 

Instead, we should consider implementing another approach for rendering the content asynchronously which would improve the user experience. 

Add UI for adding comments and ability to save them. Comments are represented in the document model as text annotations (annotations with Subtype Text). 

This would allow switching the focus between form field controls by using the Tab key.

Layers represent groups of optional content which can be hidden or shown.

Most PDF viewers have option (enabled by default) which allows fields to be highlighted with colors predefined in the settings. Required fields are highlighted using different color.

For example: In Adobe Acrobat Reader DC this is enabled in "Edit" -> "Preferences" -> "Forms" -> "Highlight Color" -> "Show border hover color for fields". 

When displaying PDF-Files using PDFViewer, ContentElementsCanvas .RenderAsync uses reflection (DispatcherObjectUtils.ApplyDispatcher) to render Visuals on multiple threads.
However this leads to a memory leak since the dispatchers cant be GC'ed, see screenshot below.




The Screenshot is from the actual application we expirienced this issue with, the attached reproduction example is a boiled down version of what your code does.
If you wanna reproduce this on your own, create an application that uses PdfViewer that switches between many pdf files. The ammount of Dispatchers will grow steadily, probably to a total of the number of threads used by Task.Factory.

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.

Represents Highlights PDF content. While the other annotations are drawn on top of the content, the highlight annotation is behind the text it highlights. In other words, it has to be inserted at a specific place in the ContentElementsUILayer. The precise place where the highlight should be placed is described in the PDF file with the BDC, MCID and EMC operators. At the moment, we have implemented a read-only rendering for all annotation types which draws the annotions separately from the page content. In the case of Highlight, the annotation is drawn below the other content. With this implementation, depending on the PDF content, the highlight annotation might be visible or it might not be because in some cases there is geometry content below the highlighted text which hides the highlight annotation appearance. 

A rubber stamp annotation displays text or graphics intended to look as if they were stamped on the page with a rubber stamp. When opened, it displays a pop-up window containing the text of the associated note.

Visualizing a page with a huge number of images (40000) freezes the application.
When switching to the FixedDocumentSinglePageViewPresenter, all the page content should be loaded so it can be later rendered. Although the images are loaded asynchronously, there are too many threads started which seems to cause the hang. Also, according to profiling results, it seems like the image caching causes performance diminishments in such scenarios. 

When users do "copy" operation, add the content to the clipboard in RTF format. This would allow to paste the text along with its formatting in text editors like MS Word.

As a <role> I want <ability> so that <benefit>.