This article explains how to resolve the problem where PDF versions of invoices or quotes contain question marks in place of letters.
To resolve this:
1. Navigate to Setup > General Settings > Invoices tab
2. Locate the PDF Font Family Setting
3. Change the setting to Freesans
4. Click Save Changes
The text should now be displayed properly:
If the problem persists after that, it indicates that the characters in use are not supported by any of the default PDF fonts included in WHMCS.
The next step is to download and install the dejavusans font. Please refer to Installing Additional Fonts for instructions.