The Factory Service Manuals (FSM's) are year specific and will basically tell you how to completely rebuild your truck in great detail. Haynes Manuals are very generic to the year range that they cover.
The FSM's are significantly more expensive, but IMO if you are serious about taking care of your rig then you will want to pick up the FSM over the Haynes manual. I have the appropriate FSM for all 4 of my rigs and I use them regularly. I have the Haynes Manual for my 1990 and since I bought the FSM it is basically just there because I had it already. Each time I have gotten a new rig, I pick up the appropriate FSM very soon thereafter.
I can't help you with the pdf, but I don't care for them myself except just to scan, in the garage, the hard copy is much more practical, that is unless you can download it onto a tablet to carry around with you and you aren't afraid to get greasy finger prints all over it.