| .RAD | Reality Pump Studios | Indstillingsfiler | Reality Adlib Tracker Module | Adlib Tracker II | Adlib Tracker II |
| .RB | Larian Studios | Indstillingsfiler | Divinity: Original Sin Game Data | Divinity: Original Sin | Larian Studios |
| .RB4 | Sarm Software | Indstillingsfiler | Resume Builder 4 File | Sarm Resume Builder | Sarm Software |
| .RCF | Rhapsody International | Indstillingsfiler | Audiogalaxy Rhapsody Storage File | Rhapsody | Rhapsody International |
| .RCT | Microsoft Corporation | Indstillingsfiler | Visual Studio Resource Template | Microsoft Visual Studio | Microsoft Corporation |
| .RDF | Unknown Developer | Indstillingsfiler | Resource Description Framework File | Mozilla Firefox | Mozilla |
| .RDG | Microsoft Corporation | Indstillingsfiler | Microsoft Remote Desktop Connection Manager Configuration | Microsoft Remote Desktop Connection | Microsoft Corporation |
| .RDI | SAFEJKA S.R.L. | Indstillingsfiler | Rohos Disk Image File | Rohos Mini Drive | SAFEJKA S.R.L. |
| .RDO | Xerox | Indstillingsfiler | Xerox Rawster Document Object File | Xerox Document Scan and Make Ready | Xerox |
| .RDP | Microsoft Corporation | Indstillingsfiler | Remote Desktop Configuration File | Microsoft Remote Desktop Connection | Microsoft Corporation |
| .RDR | Devolutions | Indstillingsfiler | Remote Desktop Manager Settings File | Remote Desktop Manager | Devolutions |
| .RDW | Mediachance | Indstillingsfiler | Real-DRAW Project File | Real-DRAW | Mediachance |
| .REG | Microsoft Corporation | Indstillingsfiler | Registry File | Windows Registry Editor | Microsoft Corporation |
| .REPX | Developer Express Inc | Indstillingsfiler | XtraReports Report Definition | XtraReports | Developer Express Inc |
| .RES | Valve | Indstillingsfiler | Valve Resource File | Half-Life | Valve |
| .RESMONCFG | Microsoft Corporation | Indstillingsfiler | Microsoft Windows Resource Monitor Settings | Microsoft Resource Monitor | Microsoft Corporation |
| .REX | Propellerhead | Indstillingsfiler | ReCycle Loop File | Avid Pro Tools | Avid Technology |
| .RFQ | Siber Systems | Indstillingsfiler | RoboForm SearchCard File | RoboForm | Siber Systems |
| .RGD | Redbeet Interactive | Indstillingsfiler | Raft Saved Game File | Raft | Redbeet Interactive |
| .RKP | Devolutions | Indstillingsfiler | RemoteKeys Profile File | Remote Desktop Manager | Devolutions |
| .RLL | Microsoft Corporation | Indstillingsfiler | Microsoft Resource Library | Microsoft Visual Studio | Microsoft Corporation |
| .RLS | Nokia | Indstillingsfiler | Symbian Localization File | Symbian SDK | Nokia |
| .RML | Autodesk, Inc. | Indstillingsfiler | Redline Markup Language File | Volo View | Autodesk, Inc. |
| .RMS | RealNetworks | Indstillingsfiler | Secure Real Media File | RealNetworks RealTimes | RealNetworks |
| .RMSKIN | The Rainmeter Team | Indstillingsfiler | Rainmeter Skin File | Rainmeter | The Rainmeter Team |
| .RNX | RealNetworks | Indstillingsfiler | RealPlayer Settings File | RealPlayer Cloud | RealNetworks |
| .ROS | Jon Taylor | Indstillingsfiler | BattleScribe Roster Editor File | BattleScribe | Jon Taylor |
| .RPB | Famatech | Indstillingsfiler | Radmin Phonebook File | Radmin | Famatech |
| .RPK | RadLight | Indstillingsfiler | RadLight Media Player Skin | RadLight media player | RadLight |
| .RPS | Autodesk, Inc. | Indstillingsfiler | 3ds Max Render Preset Settings | Autodesk 3ds Max | Autodesk, Inc. |
| .RPV | RealNetworks | Indstillingsfiler | RealPlayer Visualization File | RealPlayer | Realtime Technologies |
| .RRR | Symantec Corporation | Indstillingsfiler | Registry Mechanic Backup File | PC Tools Registry Mechanic | Symantec Corporation |
| .RSP | Rockwell Automation Inc. | Indstillingsfiler | RSLogix PLC Program File | RSLogix 5 | Rockwell Automation Inc. |
| .RSX | Red Digital Cinema Camera Company | Indstillingsfiler | Temporary Red Alert Camera Data | REDCINE-X | Red Digital Cinema Camera Company |
| .RTL | Hewlett-Packard | Indstillingsfiler | Raster Transfer Language File | SwiftView | SwiftView, Inc. |
| .RTO | Micro Focus International plc | Indstillingsfiler | Rumba File Transfer Profile | Rumba | Micro Focus International plc |
| .RTS | Heaventools Software | Indstillingsfiler | Resource Tuner Console Script | Resource Tuner Console | Heaventools Software |
| .RULESET | Microsoft Corporation | Indstillingsfiler | Visual Studio Code Analysis Rule Set | Microsoft Visual Studio | Microsoft Corporation |
| .RWF | HingePoint, Inc. | Indstillingsfiler | ReFrame Workspace | ReFrame | HingePoint, Inc. |
| .RXML | Roxen Internet Software | Indstillingsfiler | Roxen Macro Language Source Code | Sublime Text | Sublime HQ Pty Ltd |
| .RXP | Roxio | Indstillingsfiler | Easy CD & DVD Creator 6 Playlist File | Roxio Creator NXT Pro 5 | Roxio |
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