BMPR documents are de facto projects that come from wireframing tool called Balsamiq and only this software can be used to export data to PDF format.
According to Balsamiq documentation, you can export to PDF by selecting the Project ► Export... menu option, with each wireframe displayed on a separate page of a PDF document in the same order as in the project.
The PDF will be created in high resolution and with selectable text and If your wireframes contain links, these will work in your exported PDF as well.