Most printing problems are font problems. It’s an interaction between
The PDF viewer
The standards for each of them are complicated and are rarely followed exactly. That sometimes causes unexpected failures in the printing process.
Usually, the easiest thing to change is the PDF viewer. Specifically, try using Adobe’s latest.
If that doesn’t work or or is not possible, the next best move is to get a preflight report using Adobe Acrobat Pro. It will often contain errors that can lead to a solution.
Some solutions that have worked in the past are:
Use the same font, encoded differently (e.g, if TTF isn't working correctly, try an OTF version)
Use a different printer
Use a different font that looks similar