If you simply want to read the text - if you're not interested in the images - there are tools available that will extract the text from a PDF and store it in a new text file, which is usually easy to read on a tablet.
One that I've used with some success is
http://www.extractpdf.com/.
However, these tools are very hit-and-miss. The quality of the results depends on how the text is laid out, especially in relation to images and other objects. It works OK if the document contains a single flow of text. But in the worst cases, the resulting text might be completely jumbled and garbaged.
Mike