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".
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.
Matte color is used for preblending images with some background color, using the SMask. Matte color is specified using the optional 'Matte' entry for the SMask object. See PDF 1.7 specification, page 554-555: Matte array (Optional; PDF 1.4) An array of component values specifying the matte color with which the image data in the parent image has been preblended. The array consists of nnumbers, where n is the number of components in the color space specified by the ColorSpace entry in the parent image’s image dictionary; the numbers must be valid color components in that color space. If this entry is absent, the image data is not preblended.
This allows specifying a soft mask in the external graphics state.
A pop-up annotation displays text in a pop-up window for entry and editing. It typically does not appear alone but is associated with a markup annotation (its parent annotation) and is used for editing the parent’s text.
Implement import and export of content with Type0Font with GBK-EUC-H encoding.