I'm writing my solution so that it can be found via Google ...

My custom were not applied in the PDF - even when I set all options in dompdf/dompdf initialization, gave all directory permissions, etc.

We use really custom fonts, not Google fonts - which are loaded from s3 with cloudfront.

The solution was: Use ttf / truetype fonts ... woff and woff2 were not applied, even when these files were loadable.