The redaction annotation is described in the following PDF reference document:
http://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/pdf_reference_addendum_redaction.pdf

You may also see sample document with this annotation type attached.

Since LIB Version 2017.3.925 annotations of type Redact can be visualized.

When annotations have annotation flag Print they should be visualized when printing the document. Usually, Widget annotations have such flag and currently RadPdfViewer does not print them at all.

Available in LIB Version 2017.3.918.

Introduce support for Sticky Note Annotation.

Introduce support for PolyLine Annotation

Introduce support for Polygon Annotation

Introduce support for Circle Annotation

Introduce support for Square Annotation

Introduce support for Line Annotation.

This may result in seeing the pattern as a solid color or even not seeing it at all if this color is white and coincides with the background of the page.

The current implementation relies on the graphic state color to be always SolidColorBrush. However, it may be other color type and InvalidCastException is thrown. This results in missing content.

Available in LIB version 2017.1.410.

The issue is caused by memory optimization that requires loading page content only for the visible pages. 

In order to fix the issue and still benefit from the memory optimization, we are introducing setter in FixedDocumentPresenterBase VisiblePages property. Now this property needs to be set each time the visible pages are changing in custom presenter implementation. Setting VisiblePages ensures that all visible pages content will be loaded correctly.

The Form XObjects are supported in RadPdfViewer. In case anyone has messed up this feature with the one for interactive forms and form filling, please, vote and subscribe to the corresponding item at http://feedback.telerik.com/Project/143/Feedback/Details/197877 .

When having Pdf with SimpleFont that does uses glyphs with missing width their width is calculated as zero due to wrong integer calculations.

When printing a document with multiple pages, the pages that are not currently visible will be printed without content.

The fix will be available in next LIB release (v. 2015.1.0323).

We have a good news for all of you who have experienced problems with the memory consumption of RadPdfViewer. We have made significant optimization of what is cached for each page when scrolling in a document.
Please have in mind that when using big images in a document the optimization may seem not so significant. This is because there is additional opportunity to further optimization of the caching mechanism for the image sources.
I have logged this additional opportunity as a different feature request. Here is a link if you would like to subscribe for status updates of that item to: Optimize the image source cache - http://feedback.telerik.com/Project/143/Feedback/Details/189305-optimize-the-image-source-cache

The fix will be available in our official release Q2 2016.