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.
Dialog for inputting the password should be implemented in order to be able to decrypt the file content.
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".
Add support for importing and filling interactive forms. Interactive Forms content is visualized read-only in RadPdfViewer UI with R1 2017 Release Available in R3 2017 Official Release Version.
By using "Auto Detect Hyperlink" functionality RadPdfViewer should detect URLs and email addresses and turn them into hyperlinks. For instance if the PDF file contains text http://www.telerik.com/ this text should become a hyperlink.
Currently, the disabling of the scrolling functionalities in PdfViewer is pretty tricky. Expose an API that allows users to control this functionality easier (hiding the scroll bars, disabling horizontal and/or vertical scrolling). A sample of how the scrolling could be completely disabled is attached to this item.
When text is exported from PDF document using the TextFormatProvider (it's also used internally for the Copy operation), it is automatically split to lines using the vertical position of the words on the page, and small tolerance. Currently the tolerance is hard-coded to 0.1 pixels, which is not suitable for documents which contains scanned and OCR-ed text, and there the text lines could be slightly inclined. The result is that words on one slightly inclined line are recognized as if they are on separate lines.