Compress ODT documents by optimizing what makes them big
An ODT file is a ZIP archive holding your text as XML, plus every picture you've inserted, stored at its original size. The text is almost never the problem: a 50-page report might be 100 KB of text. The pictures are. A single photo straight from a phone camera can be 4 MB, and a photo pasted in as a PNG or BMP can be even larger. This compressor shrinks those images to a sensible size for a document, removes a few extras the file doesn't need, and rebuilds a valid ODT that opens exactly like the original.
Everything runs in your browser. Your documents are never uploaded.
How to use it
- Choose one or more
.odtfiles, or drag them onto the box. - Pick the largest image size and photo quality. The recommended settings suit almost any document.
- Check each result: the size savings, the verification badge, and the list of images and what happened to each.
- Download the compressed document, or all of them at once as a ZIP.
What this compressor changes
| Part of the file | What happens | Why |
|---|---|---|
| Large photos | Resized to the largest size you chose and saved again as JPEG at the chosen quality | A 1600-pixel image fills a full page width at about 250 dpi. Anything bigger is wasted in a document. |
| Photos stored as PNG or BMP | Converted to JPEG, with every reference in the document updated | These formats are meant for graphics. A photo in BMP can be ten times larger than the same photo in JPEG. |
| Logos, diagrams, screenshots | Kept as PNG, and only resized if they're larger than your limit | JPEG would blur sharp edges and text. Transparency is always preserved. |
| Preview thumbnail | Removed | Only used by file browsers. It's rebuilt the next time you save the document. |
| Saved printer setup | Removed | Driver settings for the last printer used. They can be several kilobytes and aren't needed to print. |
| Text, styles, layout, tables | Untouched | Your content is never rewritten. |
An image is only replaced when the new version is meaningfully smaller. If re-saving a picture wouldn't help, the original is kept.
Why not just "maximum ZIP compression"?
Some ODT compressors only re-pack the archive at a higher compression level, or strip all the whitespace from the XML. Neither helps much. The text in an ODT is already compressed, and higher levels typically save around one percent. Photos are already compressed formats, so zipping them again does nothing. Removing whitespace from document XML can even be risky, because spaces between words are sometimes stored exactly there. The real savings come from the pictures, which is where this tool focuses.
How each file is checked
After compressing, the tool reopens its own output and checks it the way a word processor would. It confirms that the file is a valid ODT archive with the correct structure, that every part passes its checksum, that every picture the document refers to is present and listed in the manifest, and that every edited XML part is still well-formed. The green Verified badge means all of those checks passed. In testing, compressed documents opened in LibreOffice with the same pages and text as the originals.
Frequently asked questions
Will my document look different?
Text, formatting, tables, and layout are untouched. Photos are re-saved at a size and quality that look the same on screen and in normal printing. Choose "Keep original dimensions" and "High" quality if the document will be printed large or professionally.
Are my files uploaded?
No. The document is opened, optimized, and rebuilt inside your browser. Nothing is sent to a server.
Does it work with ODS spreadsheets and ODP presentations?
Yes. They use the same OpenDocument format, so images in spreadsheets and slides are optimized the same way.
Can it compress a password-protected ODT?
No. Encrypted documents can't be changed without the password, so the tool tells you and leaves the file alone. Remove the password in your word processor first, compress, then add it back.
What about digitally signed documents?
Any change to a signed document invalidates its signature. The tool warns you when a document is signed, so you can re-sign it after compressing.
My document only got a little smaller. Why?
It probably has few or small images. Documents that are mostly text are already compact, because the ODT format compresses text automatically.