How can I adjust the fonts and layout of PDF reports?
The PDF generator uses the HTML to create the PDF. So changing CSS will have effect. But.. to have a different font in the PDF, the font should be available on the server. If the font is not available on the server (and the pdf generator) then a fall-back font is used.

Here's some more info about DOMPDF (the tool CiviCRM is using for creating PDF's):


https://stackoverflow.com/questions/12581156/custom-fonts-for-dompdf
https://github.com/dompdf/dompdf/wiki/About-Fonts-and-Character-Encoding