History Lesson: What Is a .odt File? Why Word Opens It Differently

What is a .odt file?

A .odt file is the text-document member of the OpenDocument Format (ODF), an open standard for office files. Its siblings are .ods for spreadsheets, .odp for presentations, and .odg for drawings. It is the native format of LibreOffice Writer and Apache OpenOffice Writer, and many other programs — Google Docs, Microsoft Word, Apple’s TextEdit — can open or export it. Its official media type is application/vnd.oasis.opendocument.text.

Open the bytes and the first two letters are PK, the signature of a ZIP archive — the same container format Windows uses for compressed folders. Inside, the ODF packaging rules put a small file called mimetype first, stored uncompressed, so software can recognize the document without unpacking it. Then come separate XML (Extensible Markup Language — plain text built from tags) files: content.xml for the words and tables, styles.xml for fonts and page layout, meta.xml for author and dates, settings.xml for view preferences, and a manifest listing every part, plus a Pictures folder and often a small thumbnail image. A .fodt is the “flat” variant: the same XML in one uncompressed file.

Why does Word open it, but the layout shifts?

Because Word does not edit OpenDocument directly; it translates the file into its own document model on the way in and back out on save. Microsoft’s support article on the differences between .odt and .docx says .odt files are compatible with Word and with LibreOffice and OpenOffice, “but you might see formatting differences and some Word features aren’t available in .odt files.” A companion page explains that an .odt opened in Word “might not have the same formatting as it did in the original application,” because of the differences between applications that use OpenDocument.

In practice that can show up as a line break in a new place, a table that is a little wider, a picture that sits slightly off its anchor, or a page that ends one paragraph early. The words are almost always there; it is the page geometry that drifts, because two programs with different layout engines are reading the same instructions.

ODF vs OOXML: two open standards, one confusing decade

If .odt and .docx are both ZIP-plus-XML, why are they different? Because they are rival designs from rival camps. ODF descends from the StarOffice and OpenOffice.org file format. Office Open XML (OOXML) — the format behind .docx, .xlsx, and .pptx — was Microsoft’s answer: approved by the standards body Ecma International as Ecma-376 on 7 December 2006, it collected the votes it needed at ISO in April 2008 and was published as ISO/IEC 29500 in November 2008. Each describes paragraphs, styles, and pages in its own vocabulary, so moving between them is always a conversion.

The rivalry was political as well as technical. In September 2005 the Commonwealth of Massachusetts published a technology policy requiring its executive-branch agencies to save office documents in OpenDocument by 1 January 2007; a 2007 revision added Microsoft’s Open XML as an accepted format. Debates like that one are why “ODF vs OOXML” still turns up next to “what is a .odt file.”

1985: a teenager’s word processor in Lüneburg

The story begins well before XML. In 1985 Marco Börries, then 16, founded Star Division in Lüneburg, in northern Germany. Its first product, a DOS word processor called StarWriter, was cheaper than Word or WordPerfect and found fans among students and discount PC sellers, according to Der Spiegel. StarWriter grew into StarOffice, a full suite with a spreadsheet, presentations, and more, and the company later moved to Hamburg. For the binary StarWriter files from that era, see History Lesson: What Is a .sdw File?.

Sun, OpenOffice.org, and an XML file format

In August 1999 Sun Microsystems acquired Star Division and made StarOffice free to download. On 19 July 2000, at the O’Reilly Open Source Convention, Sun announced it would release the StarOffice source code under the GNU General Public License and form OpenOffice.org — which would coordinate the code and, in Sun’s words, “the definition of XML-based file formats.” The code went public on 13 October 2000.

OpenOffice.org 1.0 arrived on 1 May 2002, sharing its code base with StarOffice 6.0. Its Writer saved .sxw files: already a ZIP package of XML, the direct ancestor of .odt. The idea was that a document format belonging to no single program would outlive any one office suite.

OASIS and ISO/IEC 26300

To make that format a true standard, it went to OASIS — the Organization for the Advancement of Structured Information Standards, a non-profit consortium that publishes open technical standards. The OASIS technical committee held its first official meeting on 16 December 2002, with members from several companies, and reshaped the OpenOffice.org XML format into the OpenDocument Format. OASIS approved ODF 1.0 as an OASIS Standard on 1 May 2005.

OpenOffice.org 2.0 followed on 20 October 2005 with OpenDocument as its default format — the moment .odt files started appearing on ordinary PCs. Meanwhile OASIS submitted ODF to the joint ISO/IEC committee; it passed its ballot on 3 May 2006 and was published as ISO/IEC 26300:2006 on 30 November 2006. ISO (International Organization for Standardization) and IEC (International Electrotechnical Commission) are the bodies behind most international standards, which is why governments could point to ODF in procurement rules.

The format kept evolving: ODF 1.1 in February 2007 with accessibility additions, ODF 1.2 in September 2011 (published by ISO/IEC in 2015), ODF 1.3 in April 2021 with digital-signature and encryption improvements, and ODF 1.4, approved as an OASIS Standard on 6 October 2025. Newer versions stay backward compatible, so a .odt from 2006 is still a valid OpenDocument file.

Microsoft gets on board

On 21 May 2008 Microsoft announced that Office 2007 Service Pack 2 would open, edit, and save ODF 1.1 files; SP2 shipped on 28 April 2009. Later versions moved up with the standard: Office 2013 supports ODF 1.2, Office 2021 supports ODF 1.3, and in 2024 Microsoft announced ODF 1.4 support in Microsoft 365. WordPad in Windows 7 and later could open .odt too. So today a double-click on .odt usually just works — with the formatting caveats above.

Oracle, LibreOffice, and Apache OpenOffice

In 2010 Oracle acquired Sun, and with it OpenOffice.org. On 28 September 2010 a group of community members announced The Document Foundation and a fork named LibreOffice. On 1 June 2011 Oracle donated the OpenOffice.org code to the Apache Software Foundation, where it became Apache OpenOffice. Both suites still save .odt by default, which is why .odt files keep being made long after the companies that started them changed hands.

Why .odt files are still on disks in 2026

Because OpenDocument became the format of choice wherever people wanted documents that no single vendor controls. On 22 July 2014 the UK government chose ODF for sharing and collaborating on government documents. In March 2026 Germany’s IT planning council adopted a set of Deutschland-Stack standards that names ODF and PDF/UA for documents. Schools, charities, Linux users, and anyone who installed a free office suite have years of .odt letters, reports, and theses.

Many of those are now legacy files: written in a suite that is no longer installed, opened in Word with a shifted layout, or needed as a .docx or PDF for someone who does not use OpenDocument. For the older office formats in the same family, see StarWriter .sdw and OpenOffice Calc .sxc; for the Word side, see History Lesson: What Is a .doc File?.

When you need a .docx or PDF instead

Renaming .odt to .docx does nothing — the parts inside are still OpenDocument XML. A real conversion reads the OpenDocument package and writes a new file. Pick DOCX when someone needs to keep editing in Word, PDF when the page must look the same everywhere, and RTF or plain text when the words matter more than the layout. Whatever you choose, look over tables, frames, and page breaks afterwards.

Legacy File Converter opens .odt and flat .fodt files on your own Windows PC and saves them as DOCX, PDF, RTF, TXT, Markdown, or HTML — nothing is uploaded, which matters when the document is a contract or a medical letter. For neighboring document lessons, see RTF, Word .doc, and StarWriter .sdw.