It “is an accurate, highly compressible 3D data format optimized to store, load, and display various 3D data, metadata, assembly structure, graphics information and Product Manufacturing Information (PMI). The PRC file format can be viewed within the free Adobe Reader when encapsulated with the Protable Document Format (PDF). It can be stored within PDF as either accurate BREP geometry or tessellated data. Because of this, it can be extracted from a PDF for use years later in CAD, CAM, CAE systems.”
Read more, including the history of PRC development, at:
The PRC File Format
The most recent publically available, free for access documentation on the PRC format can be found here. NOTE: This version is the version submitted to ISO, and is behind the ISO Draft International Standard currently in circulation; this must be purchased from ISO here. The Consortium does not have the rights to reproduce ISO documentation.