Tumbler: disabling PDF and ODF

1. Rename/delete tumbler's shared library related to PDF and ODF file:
$ sudo mv /usr/lib/i386-linux-gnu/tumbler-1/plugins/tumbler-poppler-thumbnailer.so /usr/lib/i386-linux-gnu/tumbler-1/plugins/tumbler-poppler-thumbnailer.so.bak

$ sudo mv /usr/lib/i386-linux-gnu/tumbler-1/plugins/tumbler-odf-thumbnailer.so /usr/lib/i386-linux-gnu/tumbler-1/plugins/tumbler-odf-thumbnailer.so.bak

Replace i386 to x86_64 if you have 64 bit OS.

2. Regenerate thumbnails:
$ rm ~/.thumbnails