The document viewer supports the following formats:
Comic Book Archive (.cbr and .cbz)
Device Independent file format (.dvi)
DjVu (.djvu, .djv)
OpenOffice Presentation (.odp)
Portable Document Format (.pdf)
PostScript (.ps)
Scalable Vector Graphics (.svg)
Tagged Image File Format (.tiff, .tif)
Other Image Files (.gif, .jpeg, .png)
In some Linux distributions, not all formats are supported by default, so you might not be able to view all the formats listed above.
Support for a format is called a backend. If you get the error "Unable to Open Document", you may wish to check whether the backend package for the format is installed.
