Since the PDF library is not a free software, it isn’t included with the distribution of Chromium.
To get PDF support in Chromium:
- download the appropriate DEB package for your system from https://www.google.com/intl/en/chrome/browser/
- using the archive manager, extract libpdf.so from /opt/google/chrome/
- copy that file into /usr/lib/chromium-browser/ (remember you have to root or use sudo)
- restart Chromium if you have it