| wyn | WYNN Document |
| wyx | WYNN Document |
| wzn | WhizFolders Note Document |
| x3d | X3D Scene |
| x3db | X3D Binary Scene |
| x3dbz | Compressed X3D Binary Scene |
| x3dv | X3D Classic VRML |
| x3dvz | Compressed X3D Classic VRML |
| x3dz | Compressed X3D Scene |
| x3g | MakerBot X3G Document |
| xav | Final Draft AV v2 Document |
| xbc | SMART Notebook Document |
| xbdoc | Xiosis Scribe Document |
| xbel | XBEL Bookmark |
| xbk | SMART Notebook Document |
| xbmml | BMML File with Metadata |
| xbplate | Xiosis Scribe Template |
| xbrl | eXtensible Business Reporting Language |
| xbt | SMART Notebook Template |
| xcm | Concept Map |
| xddm | OpenVSP v2 VSP Design Document |
| xdes | OpenVSP VSP Design Document |
| xdoc | QuarkXPress 3.0 Document |
| xdot | Graphviz DOT File |
| xdp | XML Data Package |
| xdr | XML-Data Reduced Schema |
| xdv | XeTeX Extended DVI Document |
| xdw | Xerox DocuWorks Document |
| xfa | XML Forms Architecture Document |
| xfd | XFDL Document |
| xfdf | Adobe Acrobat XFDF Document |
| xfdl | XFDL Document |
| xfo | XSL-FO Formatted Form |
| xfp | Microsoft InfoPath Property Promotion |
| xgl | XGL 3D CAD Model |