There is no PDF available for Tiki12. The last book-like documentation was the printed manuals for the "Tiki Essentials" and the "Tiki for Smarties" books.
And generating a single pdf out of BIG doc.t.o structures is not working as expected (mainly due to issues with maketoc's, and such.
You'll have to stick with online documentation in https://doc.tiki.org , or the nice books from Rick Sapir named above.
Welcome to improve this situation, if you can (specially if you code)
P.S: The last full pdf from a Tiki version was from Tiki 1.9, compiled by me, many years ago. Maybe this can help you, specially if you are not used with the basic concepts and you want to have a free/cc-by-sa pdf handy with the basics?: