| R | Macintosh Resource Compiler |
| R | Fortran Preprocessor Source Code |
| R | Sourcer Disassembler |
| R | Pegasus Mail Resource File |
| R?? | RAR Compressed File (?? can be 01 to 99) |
| R33 | Train Simulator Game File |
| R8 | Flight Simulator Texture File |
| R8L | LaserJet Landscape Font |
| R8P | LaserJet Portrait Font |
| RA | RealMedia File |
| RAD | Reality AdLib Tracker |
| RAM | RealMedia Metafile |
| RAR | RAR Compressed Archive |
| RAS | Sun Raster Graphic |
| RAT | Rating System File |
| RAW | RealAudio Sound |
| RAW | RAW RGB 24-bit Graphic |
| RAW | Raw signed PCM Data |
| RAX | Image File |
| RB | RocketEdition File |
| RB1 | R:Base Database (RB1...RB4) |
| RBF | R:Base Data File |
| RBH | RoboHelp Project Configuration |
| RC | Microsoft Windows Resource Compiler |
| RC | Borland C++ Resource Compiler Script File |
| RC2 | Microsoft Windows Resource Compiler |
| RCD | PC Anywhere Recorded Session File |
| RCG | Netscape Newsgroup File |
| RCT | Microsoft Windows Resource Template |
| RCV | Microsoft Windows Resource Compiler |
| RD1 | Descent1 Registered Level File |
| RD3 | Ray Dream Designer Graphics |
| RD3 | CorelDream 3D |
| RD4 | Ray Dream Designer Graphics |
| RD5 | Ray Dream Designer Graphics |
| RDB | TrueVector Rules Database |
| RDB | ZoneAlarm Rules Database |
| RDF | Resource Description Framework File |
| RDF | Chromeleon Report Definition |
| RDI | Bitmap Picture |
| RDL | Paradox |
| RDL | Symbian Recogniser Library |
| RDL | Descent Registered Level |
| RDO | Raster Document Object. Proprietary file type used on Xerox Digipath Scan and Makeready workstations |
| RDX | Borland Reflex Database |
| REC | Windows Recorder Macro |
| REC | RapidComm Voice File |
| REC | Sprint Record File |
| RED | Clarion Modula-2 |
| REF | Reference (various) |
| REG | Registration Data (various) |
| REM | Annotation |
| REP | Text Document |
| REP | Report File (various) |
| REP | Blizzard Entertainment Replay File |
| REQ | Request |
| RES | Resource File (various) |
| RES | Valesco import/export text Resource file |
| REV | FrameMaker Document |
| REV | WinRAR Recovery Volume File |
| REX | OS/2 Rexx Source Code |
| REX | Oracle Report Definition |
| REZ | Resources (various) |
| REZ | Game Archive (various) |
| RF | FrameMaker Document |
| RF | RealFlash Clip |
| RF | Sun Raster Graphic |
| RFD | RecogniFORM Form Definition |
| RFG | RFG Integrator System Database |
| RFH | RFG Integrator Householding Database |
| RFT | Revisable Format Text |
| RGB | Picture File |
| RGN | Championship Manager Game File |
| RGS | Script for Windows Registry |
| RH | Microsoft Windows Resource Compiler Header |
| RI | Lotus File |
| RIA | Alpharel Group IV Raster Graphics File |
| RIB | 3D Reality Image |
| RIC | Ricoh Fax Document |
| RIF | RIFF Resource Interchange File Format |
| RIF | MetaCreation's Painter Image |
| RIP | Remote Imaging Protocol Image |
| RIX | RIX Paint Programs Image |
| RIX | Colorix File |
| RL1 | Descent1 Registered Level |
| RL2 | Descent2 Registered Level |
| RL4 | Bitmap Picture |
| RL8 | Bitmap Picture |
| RLA | Wavefront Raster Image |
| RLA | Advanced Visualizer File |
| RLB | Harvard Graphics File |
| RLC | Image Systems CAD Overlay |
| RLE | Run-Length Encoded Bitmap |
| RLZ | Computer Associates Realizer Source Code |