First enable the module "dompdf library handler"
After that you have to add the corresponding dompdf module. Sadly the straight forward way did not work in our case. But we found a corresponding solution (Post number 11) on the page https://www.drupal.org/node/850098.
Copy the dompdf module into the following directory: ...\sites\all\modules\print\lib
The mentioned PHP lib can be downloaded using this link:
https://www.versioneye.com/php/phenx:php-font-lib/0.2.2