mPDF support:

  The recommended version of this tool is 7.1.0 or newer since it is fully
  compatible with PHP 7.1, and security support has ended for all prior
  versions of PHP as of December 31, 2018.

  1. Download mPDF from https://github.com/mpdf/mpdf/releases.
  2. Extract the contents of the downloaded package into one of the
  supported paths.
  3. If using mPDF 7.0 or later run 'composer install' in the mpdf directory.
  4. To be sure your environment is set up correctly, check the Requirements
  page at https://mpdf.github.io/about-mpdf/requirements-v7.html. The PHP
  mbstring extension (including mbregex, which needs to be explicitly enabled
  in some environments) and gd extension have to be loaded.
  5. If upgrading from version 6 or older, visit the settings page on your
  site at http://example.com/admin/config/user-interface/print/pdf and select
  the new path for the "PDF generation tool" setting.
  6. Check https://mpdf.github.io/ for further information.