Although this is a very old topic, I still think it is a relevant question.
Indeed a pdf reader for piCore would be very welcome as this allows one to read some documentation whilst working on something else for instance.
The only 'workaround' that I found so far is using ghostscript which allows you to walk through a document in one direction.
I looked into many 'small' PDF readers but none of these are easy to pull in on piCore due to missing dependencies (most notably Qt framework). Ghostview (GV) would be the most obvious choice.
Any help is still very much appriciated.
Kind regards,
Pengo