) method returns only the supported extensions. As the format providers responsible for import/export are shipped in separate assemblies, if the respective assemblies are not added to your project, the method will not return those extensions.
The documentation regarding Import/Export is located here
. You can find information on the supported formats (note that PDF is not
a supported import
format), required assemblies as well as sample code.
On a side note, if you wish to display PDF files, you can try RadPdfViewer which is intended for that. I suggest you check the online demo here
and the documentation of the control here
Let us know if you need further assistance.