Thanks, I did know about github, but finding the PHP version allowed was a part of the problem.
Using your link I think I figured it out.
The travis.yml file has that information. So I looked at various commits going back and could see the descriptions.
This one dated Aug 8 had "mpdf supports only PHP 5.6+ -> fix travis "
When I looked at the Code I could see the lowest it would support is PHP 5.6
https://github.com/splitbrain/dokuwiki-plugin-dw2pdf/commit/dad1b6b1c82d1ac448bc188edb7230d441e956f5
So I have to go earlier... to March 7, 2016
"Test on current PHP" has version 5.3 listed.
https://github.com/splitbrain/dokuwiki-plugin-dw2pdf/commit/789a426649608aad03bccec517305e57417e2f3f
https://github.com/splitbrain/dokuwiki-plugin-dw2pdf/tree/789a426649608aad03bccec517305e57417e2f3f
Which drops a lot of good programming....but that is what will work.
Actually the Release 4-17-2016 might be a better choice.
https://github.com/splitbrain/dokuwiki-plugin-dw2pdf/tree/0053588555c6f8896e594e4255da2764a50b752c
Now I have to do the same for siteexport.
This version supports PHP 5.3
https://github.com/rgleason/dokuwiki-plugin-siteexport/tree/0dec81bd0253641406cd893b2fe6ecda5583d618