We have found one software suitable in our database for this conversion.
OrgPlus Enterprise can publish its own organization charts (.opx) in PDF format and it seems that this is the only way how to achieve this export.
As for the older Microsoft charts (also .opx files), if you have access to Office 2003, you can probably print them to PDF file using a virtual PDF printer installed.
OPX
Files with opx extension can generally be found as saved organization charts from Microsoft Office, or similar program that uses the same suffix, like OrgPlus.
PDF
A pdf file extension is mainly used for Adobe Portable document format, commonly referred to as PDF. All programs that create some sort of documents or projects offer the possibility to export their format to PDF format. A free PDF viewer (Adobe Reader) is available for download from Adobe website.