| unix | Unix Readme Document |
| unx | Unix Text |
| uof | Uniform Office Format Document |
| uop | Uniform Office Format Presentation |
| uos | Uniform Office Format Spreadsheet |
| uot | Uniform Office Format Text |
| up3 | UP! Printer 3D Model |
| updf | UltraPdf Publication Document |
| urdf | Universal Robotic Description Format Document |
| us | English Language Info File |
| utf | UTF-8 Encoded Text File |
| utf8 | Unicode UTF8 Encoded Text Document |
| utxt | Unicode Text File |
| uvl | UVLayout Document |
| uxdc | Microsoft Office XML Data Source |
| uxf | UML eXchange Format File |
| uxy | Orchida Embroidery System Design |
| uzed | Compressed Unicode GEDCOM Document |
| v2d | ViaCAD 2D Drawing |
| v3d | ViaCAD 3D Drawing |
| v3v | Vector Art 3D Model |
| vbk | Visual CADD Backup |
| vc | VisiCalc Spreadsheet |
| vc6 | Ashlar-Vellum Graphite Document |
| vcard | VCard File |
| vcd | Visual CADD Drawing |
| vce | Visual CertExam Exam Data |
| vcf | VCard File |
| vcg | VCG Graph |
| vclip | VinylMaster Clipart Data |
| vcp | ViaCAD Pro Drawing |
| vcs | vCalendar Document |
| vcz | Pictures by PC Compressed Drawing |
| vda | VDA-FS CAD Document |
| vdcl | VectorDraw Compressed Drawing |
