| oft | Microsoft Outlook Template |
| ofx | Open Financial Exchange Document |
| ognc | Dynamic Web Page |
| ol | PTC Creo Model File |
| ola | Online Access |
| olf | OyezForms Legal Document |
| olfx | OyezForms 10 Document |
| oli | Olivetti Text Document |
| olv | OyezForms Legal OLV Document |
| om | Configura Drawing Document |
| omd | MindView for Mac Document |
| oml | TracePro Model |
| omp | OpenMind Document |
| omv | Jamovi Document |
| onb | OpenModelica Notebook |
| one | docPointer Visual ReadMe Data |
| Microsoft OneNote Document |
| oo3 | OmniOutliner 3 Document |
| oo3template | OmniOutliner 3 Document Template |
| oog | Object Oriented Graphics Library |
| oogl | Object Oriented Graphics Library |
| oos | OpenOffice.org Spreadsheet |
| oot | OpenOffice.org Text |
| opd | OmniPage Document |
| opeico | Opeico Text Data |
| openbsd | OpenBSD related Readme Text |
| oplx | OmniPlan Document |
| opml | Outline Processor Markup Language File |
| opsx | Open Pedigree Standard Exchange Document |
| opt | PhotoScore Document |
| opw | OrgPlus Organization Chart |
| opx | Microsoft Organization Chart Document |
| opxt | OrpPlus Template |
| oqy | Microsoft Excel OLAP Query |
| or5 | Lotus Organizer 5 Document |
| or6 | Lotus Organizer 6 Document |
| ort | IBM Rich Text Editor Document |
| osc | OptionScope Worksheet |
| osg | OpenSceneGraph Scene |
| osgb | OpenSceneGraph Binary Scene Data |
| osgt | OpenSceneGraph ASCII Scene Data |
| otc | OpenDocument Chart Template |
| otf | OpenDocument Formula Template |
| oth | OpenDocument HTML Template |
| otln | Opal Outline Document |
| otm | Origin Matrix Book Template |
| otmu | Origin Unicode Matrix Book Template |
| otp | OpenDocument Presentation Template |
| Origin Graph Template |
| otpu | Origin Unicode Template |
| ots | OpenDocument Spreadsheet Template |
| ott | OpenDocument Text Template |
| otw | Origin Worksheet Template |
| otwu | Origin Unicode Worksheet Template |
| otx | Olivetti Olitext Plus Document |
| ov | OrgPlus Chart |
| ov6 | Sharp Printer Overlay Document |
| ovd | Ovation 1 Document |
| ove | Overture Musical Score |
| ovex | Overture v5 Score |
| ovp | The Overlay Maker Package |
| ovr | The Overlay Maker Overlay |
| oxps | OpenXPS Document |
| p2d | PointLineCAD 2D Document |
| p2s | PhotoWorks Scene File |
| p3d | PointLineCAD 3D Document |
| p3i | Pixie Document |
| p3l | PointLineCAD 3D Drawing Layer Data |
| p5d | DynaCAD v5 Parts Document |
| p65 | Adobe Pagemaker 6.5 Document |
| p6d | DynaCAD v6 Parts Document |
| p9s | Plane9 Scene |
| pages | Apple Pages Document |
| pages-tef | Apple Pages iCloud Document |
| paper | Dropbox Paper Document |
| par | Solid Edge Parts Document |
| partout | PARTOUT Presentation |
| pat | MultiMate Pattern Data |
| PC Stitch Pattern |
| patt | ARToolKit Pattern |
