Compress ODT documents in your browser
OpenDocument files are ZIP packages, and the weight usually sits in Pictures. We re-encode those raster images and rebuild the package without laying out or rewriting your document.
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No ODT to hand?
How to compress an ODT document
It is opened in this tab and stays on your machine. There is no upload endpoint waiting for the document.
75% at 1600px is generous for a page or screen and usually takes a photo-heavy document down by half or more.
The result reports the pictures it recompressed and the recognised artwork it could not safely touch.
The output remains a standards-based .odt for LibreOffice Writer, OpenOffice, Collabora and other OpenDocument applications.
What is actually inside an .odt
An .odt is an OpenDocument ZIP package. The writing, styles, settings and metadata live in XML files, while embedded raster images normally live under Pictures. Its first entry is a small uncompressed mimetype part that tells an office application exactly what package follows.
Text is cheap and pictures are not. Writer can display a phone photo at postcard size while retaining every original camera pixel inside the document. A short illustrated letter, report or manual can therefore be almost entirely image data even though the page itself looks modest.
This tool decodes JPEG and PNG parts from Pictures, writes each one back as the same format under the same name and rebuilds the package with mimetype first and uncompressed. Content XML, styles, page layout, tracked changes, comments, fields, tables and references are not interpreted.
A text-only ODT already benefits from ZIP deflate and has little spare weight. Repacking it may recover a few per cent, but deleting document content for a more impressive number would be dishonest. The result says how many pictures were actually available to change.
ODT document compression FAQ
Why is my ODT document so large?
Usually because Writer kept full-resolution copies of pasted photos or screenshots in the Pictures folder. The words, styles and settings are XML and compress well; one phone photograph can outweigh hundreds of pages of ordinary prose. Embedded fonts and vector artwork can also be heavy, but rewriting either could change the page.
Will the compressed ODT keep its formatting?
Yes. Content, styles, tables, page breaks, fields, comments and tracked changes are carried through without being laid out again. JPEG and PNG parts keep their original format and package name, so image anchors still point to the same places. Only their invisible pixel detail changes at the quality and width you choose.
Why does the mimetype entry matter?
The OpenDocument packaging rules put a part named mimetype first in the ZIP and store it uncompressed. Applications can then identify the file without scanning the whole archive. The writer used here preserves the source order and enforces that first-entry storage rule, rather than treating an ODT as an arbitrary ZIP download.
What happens to EMF and WMF drawings?
They are left untouched. EMF and WMF are vector formats, so rasterising them behind your back would soften lines and text and could alter printing. SVG, GIF and TIFF parts are also retained as supplied because the engine only has a safe same-format path for JPEG and PNG. Recognised drawings are counted in the result.
What does “squeeze screenshots harder” do?
It reduces embedded PNG files to a palette of no more than 256 colours before writing them again. Screen captures, charts and flat diagrams generally use few colours and compress far better this way. Photographs saved as PNG may show faint steps in smooth gradients, so the option is deliberately off by default.
Can it open a password-protected or encrypted ODT?
No. Encryption applies to the package parts themselves, and rebuilding only the entries that happen to be readable would produce a broken document. A protected ODT is refused. Save an unencrypted copy in LibreOffice first if you are authorised to remove its password.
Why did my text-only ODT barely shrink?
Because XML text is already deflated inside the package and is remarkably small. The large savings come from JPEG and PNG pictures under Pictures. If none are present, rebuilding the archive is worth only a few per cent, and the tool returns the original when its rebuilt version would be larger.
Is my ODT uploaded anywhere?
No. JavaScript in this tab reads the ZIP package, re-encodes eligible pictures and writes the download directly from memory. Your document never becomes a request to a remote server.
Related
Same format joins the queue. Anything else re-routes to its own tool.