This article describes common problems that can be encountered when using RadPdfViewer and their solutions.
There are several perquisites that have to be fulfilled in order for a PDF file to be loaded correctly. Some of them are listed here.
When retrieving a file as a byte array from database and creating a MemoryStream from it, there are cases when the retrieved file is not shown correctly. This is usually due to additional NULL(0) bytes appended to the end of the document when it was stored in the database.
PDF files have to end with %%EOF marker, so this essentially makes the document invalid and RadPdfViewer is unable to show it. RadPdfViewer is looking for this marker in the last 1024 bytes and if it does not find it, throws an exception.
In order to fix the issue, you can manually trim the additional (null) bytes.