| Endung | Registry-Eintrag | Anwendung (Standard) |
| .x | text | MICROSOFT Notepad |
| .x32 | MacromediaXtra32 | Macromedia Erweiterung |
| .xbm | image/x-xbitmap | |
| .xhtml | htmldatei | MICROSOFT Internet Explorer |
| .xla | Excel.Addin | MICROSOFT Excel |
| .xlb | Excel.Sheet.8 | MICROSOFT Excel |
| .xlc | Excel.Chart.8 | MICROSOFT Excel |
| .xld | Excel.Dialog | MICROSOFT Excel |
| .xlk | Excel.Backup | MICROSOFT Excel |
| .xll | Excel.XLL | MICROSOFT Excel |
| .xlm | Excel.Macrosheet | MICROSOFT Excel |
| .xls | Excel.Datenblatt.8 | MICROSOFT Excel |
| .xlshtml | Excelhtmldatei | MICROSOFT Excel |
| .xlt | Excel.Template | MICROSOFT Excel |
| .xlthtml | Excelhtmltemplate | MICROSOFT Excel |
| .xlv | Excel.VBAModule | MICROSOFT Excel |
| .xlw | Excel.Workspace | MICROSOFT Excel |
| .xml | text | MICROSOFT Notepad |
| .xnk | xnkdatei | |
| .xpl | RealPlayer.MP3PL.6 | Real Player |
| .xprm | COASTWebMaster.Document | COASTWebMaster |
| .xsl | text | MICROSOFT Notepad |
| .xxe | WinRAR | Winrar |
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