evince по дефолту, а вообще:
$ aptitude search ~ddjvu~dview
p djview3 - Viewer for the DjVu image format
p djview4 - Viewer for the DjVu image format
i evince - Document (postscript, pdf) viewer
p evince-dbg - Document (postscript, pdf) viewer - debugging symbols
p gscan2pdf - A GUI to produce PDFs from scanned documents
p libevdocument-dev - GNOME document viewer backend library - development headers
i libevdocument1 - GNOME document viewer backend library
p libevview-dev - GNOME document viewer view library - development headers
i libevview1 - GNOME document viewer view library
p okular-extra-backends - additional document format support for Okular