Create png thumbnails from postscript and pdf documents
evince-thumbnailer [-s size] input output
evince-thumbnailer is a GNOME program to create thumbnails from PostScript (PS), Portable Document Format (PDF), DjVu and DVI files.
evince obeys all normal GNOME and GTK+ command line options. The only option -s size makes it possible to choose the vertical size of the created thumbnail.
evince(1), gnome-options(7), gtk-options(7).
http://www.gnome.org/projects/evince/