Almost every program nowadays supports Export to PDF and FileMaker Pro relational database management system is no exception in this.
An export to PDF format is is essentially what fp3 to pdf conversion represents and it is typically used for export of tables and other printable data collections.
Unfortunately, we do not know about any other way to convert fp3 to pdf or about any free online fp3 to pdf converter, so using FileMaker seems like the only choice.
The same goes for FastReport Studio that uses it's own unique .fp3 file (same suffix, different file type) for reports which may be printed as PDF documents.