If you have created a PDF file by scanning documents, then DJVU might be a better format for that. Converting a PDF file to DJVU is easy on Ubuntu.
Install the pdf2djvu package:
$ sudo apt install pdf2djvu
To convert a PDF file to DJVU:
$ pdf2djvu foo.pdf -o foo.djvu
Tried with: PDF2DJVU 0.7.17 and Ubuntu 14.04