When importing a document with empty pages collection an ArgumentNullException: 'Value cannot be null.
Parameter name: page', is thrown, which leads to application crash.
Workaround: Import the document using the PdfProcessing library and add an empty page:
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.
RadPdfViewer does not read image resources defined in Form XObject elements.
This happens only in scenarios when the widget has On state appearance defined and Off state appearance missing. If both appearances are missing then RadPdfViewer recalculates the appearances and the checkbox is successfully selected and deselected.