The File Nobody Could Open
You wrote something in LibreOffice, Google Docs, or whatever free word processor came with your laptop. You hit save, attached the file to an email, and sent it off. Twenty minutes later the reply comes back: "This opened all weird — the spacing is off and some of the headings are gone. Can you resend it as a Word doc?"
The file you sent was almost certainly an ODT. The file they wanted was a DOCX. And the reason the two keep tripping people up isn't that one is "better" — it's that they come from two different worlds that quietly compete for the same job: being the default way you save a document.
Here's what actually separates them, which one you should save in, and what to do when you've got the wrong one.
What ODT and DOCX Actually Are
Both are modern, zip-based document formats. If you rename either one to end in .zip and open it, you'll find a bundle of XML files, images, and style definitions inside. That shared design is why converting between them is usually clean — they're describing the same kinds of things, just in slightly different dialects.
The difference is who made the dialect.
DOCX is Microsoft Word's format. It arrived with Office 2007, replacing the old binary DOC, and it's built around the Office Open XML standard. Because Word runs on the overwhelming majority of office computers, DOCX became the de facto language of documents. When someone says "send me the Word file," they mean DOCX.
ODT is the OpenDocument Text format. It's the native format of LibreOffice, OpenOffice, and a long list of free and open-source writing tools. It's an open standard (ODF) that isn't tied to any single company. Google Docs, Apple Pages, and even Microsoft Word can all open and save it — but none of them treat it as the first-choice default.
So the split is simple: DOCX is what Microsoft's ecosystem produces, ODT is what the open-source ecosystem produces, and your word processor picked one for you without asking.
Why ODT Keeps Opening "Wrong" in Word
Here's the frustrating part. Microsoft Word can open ODT files. It just doesn't love them.
When Word imports an ODT, it has to translate the OpenDocument styles into its own internal model. Most of the time this goes fine. But the edges get rough: custom heading styles can lose their formatting, spacing and indentation can shift, numbered lists sometimes restart or renumber, and anything fancy — footnotes, tracked changes, embedded fonts, complex tables — is where the translation most often slips.
The reverse happens too. A DOCX opened in LibreOffice can drift slightly, especially with heavily formatted layouts. Neither translation is broken, exactly; it's that each app is fluent in its own format and merely conversational in the other.
This is why "it looked fine on my screen" is such a common refrain. On your machine, in the app that created it, the file is perfect. The problems only appear when it lands in a different app that has to translate.
Which One Should You Save In?
Match the format to where the document is going.
Use DOCX when the document is leaving your hands
If you're sending a resume, a cover letter, a contract draft, an assignment, or anything to a coworker, client, teacher, or recruiter, save it as DOCX. It's the format everyone can open, it's what applicant-tracking systems and submission portals expect, and it's the one least likely to come back with "can you resend this?"
Most free writing apps let you pick the format in the Save As or Export menu. In LibreOffice it's File, then Save As, then choose "Word 2007-365 (.docx)." If your app already saved an ODT, you don't have to retype anything — run it through ODT to DOCX and you'll get a clean Word file in a few seconds.
Use ODT when you're staying in the open-source world
If you and everyone who'll touch the document use LibreOffice or OpenOffice, ODT is the better native choice. It preserves those apps' formatting perfectly because it's their mother tongue, it's an open standard that won't get locked behind a subscription, and it tends to produce slightly smaller files. For personal drafts, open-source team workflows, or long-term archiving where you don't want to depend on one company's format, ODT is a genuinely good call.
Use neither — send a PDF — when it's final
If the document is finished and nobody needs to edit it, the format war doesn't matter. Export a PDF and the layout freezes exactly as you see it, on every device, in every app. Convert straight from ODT to PDF or DOCX to PDF. This is the single best way to stop "it looks wrong on my computer" emails, because a PDF doesn't get re-translated by the reader's software — it just displays.
How to Convert Without Wrecking the Formatting
A few things make conversions come out clean:
If you've inherited an even older file — a legacy .doc from Word's pre-2007 era — convert it up to the modern format first with DOC to DOCX, then work from there. The old binary DOC format is the one most likely to open with scrambled formatting in anything made this decade.
The Quick Decision Guide
Bottom Line
ODT and DOCX aren't rivals where one wins. They're the same idea — a zipped bundle of XML describing your document — spoken in two dialects, one from Microsoft and one from the open-source world. Each is flawless in its home app and a little lossy when a different app has to translate it.
The practical rule is almost boring: save in the format of wherever the file is going. DOCX when it's leaving for the wider world, ODT when you're staying in open-source tools, PDF when it's final. And when your app handed you the format you didn't want, you don't start over — you convert it in a few seconds and get back to the actual work.
The document was never the problem. The dialect was.