You can change the font size by clicking the option in the link bar at the top of the page or in the box on this page. The box also gives general access keys for the site and keys to change style on the fly. The changes will be persistent across pages during any visit to the site.
Adobe also provides access pages with lots of information including a free translation service intended to make PDFs accessible to screen readers.
Some of the material in the PDFs on this site is technical and I cannot vouch for how well the readers do on this.
There are now many providers of software tools for reading and otherwise manipulating PDFs. Googling “pdf shareware” turns up many options.
Some of the files on this site are ZIPed files. Typically, these will be multiple files compressed into a single file for the purposes of distribution. PKWARE is a standard source for downloadable software to expand these ZIPed files.
Alternatively, there is very good shareware for dealing with ZIPed files. I am a big fan of the software provided at Info-ZIP.
If you come across gzip'ed files (ending in .gz), you can uncompress them
with the command
gzip -d filename. gzip will be available
on UNIX systems. You can also get a DOS/windows command line version.