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Office file formats are the structures and filename extensions used to save and exchange documents, spreadsheets, and presentations. The familiar defaults—DOCX, XLSX, and PPTX—are XML-based formats; macro-enabled counterparts use DOCM, XLSM, and PPTM. The extension alone does not guarantee that every app will display or preserve a file’s features the same way.
What is a DOCX file?
A DOCX file is a Word document saved in Microsoft’s default XML-based Office format. The related defaults are XLSX for Excel workbooks and PPTX for PowerPoint presentations. Microsoft describes the underlying markup languages as WordprocessingML, SpreadsheetML, and PresentationML. These formats structure document content and features so compatible applications can read and write them.
The format references cover Office LTSC 2024, Office LTSC 2021, Office 2019, and Office 2016 for the general format tables; the extension reference is scoped to Office 2019 and Office 2016. Those scopes should not be treated as a guarantee for every Office release or third-party application. See Microsoft’s file format reference and XML extension reference.
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DOC is an older binary Word format; DOCX is the modern XML-based default. Excel’s corresponding legacy and modern formats are XLS and XLSX, while PowerPoint uses PPT and PPTX. Legacy files remain relevant when opening older documents or converting them, but choosing DOCX, XLSX, or PPTX is generally appropriate when the people exchanging a file use compatible modern software and do not need a legacy workflow.
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PDF serves a different purpose: it preserves a rendered layout for sharing rather than acting as the best editable source. Pagination may not correspond perfectly to the original document, so check the exported result before relying on it for exact page layout. Microsoft describes these distinctions in its format reference.
Which Office file extension should you use?
| Format family | Word | Excel | PowerPoint | What it means |
|---|---|---|---|---|
| Modern default Open XML | .docx | .xlsx | .pptx | XML-based defaults; cannot store VBA macro code. |
| Macro-enabled Open XML | .docm | .xlsm | .pptm | Can store VBA macro code. |
| Strict Open XML | .docx | .xlsx | .pptx | Uses the same extensions but conforms to the ISO Strict profile. |
| OpenDocument | .odt | .ods | .odp | OpenDocument text, spreadsheet, and presentation formats. |
| Legacy binary | .doc | .xls | .ppt | Older binary formats used in legacy documents and conversion workflows. |
| Fixed-layout sharing | Useful for sharing a rendered result, not usually the editable source. |
When do you need DOCM, XLSM, or PPTM?
Use a macro-enabled format when a Word document, Excel workbook, or PowerPoint presentation needs to store VBA macro code. The M suffix identifies the macro-enabled counterpart: DOCM, XLSM, or PPTM. The default DOCX, XLSX, and PPTX formats cannot store VBA code.
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A macro-enabled extension does not prove that a file contains a macro. For example, Microsoft notes that a macro-enabled Word template is configured to support macro storage but does not necessarily contain code. Microsoft’s XML filename extension reference describes the distinction.
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What does Strict Open XML mean?
Strict Open XML is an ISO/IEC 29500 Strict profile. In the Microsoft extension reference, it uses the same DOCX, XLSX, and PPTX extensions as the familiar defaults, so the filename alone does not identify which profile a file follows. The Strict profile omits features designed for backward compatibility with existing binary documents, and Microsoft cautions that some features may work differently.
Strict conformance is a standards distinction, not a promise that every application will handle the file identically. For technical background, see Microsoft’s extension reference and its Office implementation information for ISO/IEC 29500.
Can Word open an ODT file?
Microsoft lists ODT for Word, ODS for Excel, and ODP for PowerPoint as OpenDocument formats usable in the supported Office versions described in its format reference. Office can open or save these formats, but formatting or other information may be lost when a file is saved and reopened. That is a possibility, not an inevitable result; inspect the document after conversion, especially if it depends on precise layout or application-specific features.
Microsoft’s documented support applies to the Office versions listed on its file format reference; it does not establish identical behavior in all applications.
Why does formatting change when I open an Office file in another program?
A shared format specification does not mean every program implements every feature in it. An application must support the relevant markup and features, and applications may have different feature sets. Microsoft puts the point this way: “In other words, interoperability is a function of support both in the file format and by applications.” See Introduction to markup compatibility.
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When exchanging files, check the features that matter in your specific workflow—such as layout, formulas, charts, or animations—in both the program that creates the file and the one that will open it. The cited references establish that compatibility can vary, but they do not provide exhaustive feature-by-feature tests across third-party applications.
Can Office for the web edit every Office file type?
No. Viewing, editing, and conversion behavior varies by web app and file type, so check Microsoft’s Office for the web service description when a workflow depends on a particular format. For example, its matrix lists DOCX as viewable and editable, while legacy DOC is viewable and converted to DOCX for editing; ODT is listed as viewable and editable. The service matrix can change, so consult it directly for the current support details.
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