As mentioned in What is a Document? - scanned documents play a central role in Papermerge DMS. Technically, scanned document can be stored in a plethora of file formats. Papermerge DMS 2.1 works only with PDF files.
Before version 2.1 Papermerge DMS had support for PDF, TIFF, JPEG, PNG formats.
Support for TIFF, JPEG and PNG file formats will be re-introduced in later versions.