The standardized aspects of PDF are fairly universal however, there are some non-standard advancements that have been added to the format, both by Apple, Adobe, and others. If someone forgets to check the setting for embedding a specific font, then that font may not show up on a system that does not have it.
To Fix this Problem:
Click onDebtors
Invoices menu option
Double click on the invoice to open
Click Print
Click on the PDF icon
vi. In the Export to PDF window, make sure the Embedded fonts check box is ticked
vii. Click OK
viii. Save invoice to the appropriate file location