Specific document types, in particular Adobe PDF and the family of Microsoft Office documents (Word, Excel, and PowerPoint) can be encrypted and password protected, i.e. may require a password to open them (do not confuse this with the password protection against document editing).
Not a long time ago GroupDocs.Viewer for .NET was not able to display such encrypted documents. For the first time, support for encrypted PDF and Microsoft Word document was introduced in GroupDocs.Viewer for .NET version 2.16. And in version 2.17 we’ve added support for password-protected Microsoft Excel and PowerPoint documents along with additional encryption-related features.
Recently we’ve prepared a detailed article describing how to work with encrypted documents in different scenarios and use cases and would like to share it with you – please read it in our documentation section.