The open standard, converted openly
OpenDocument Text is what LibreOffice and OpenOffice write by default, and it is the format many governments and public bodies require for documents precisely because it is an open standard rather than one company's file layout. Google Docs exports it as well.
The practical consequence is that people are regularly sent .odt files they cannot open — Word handles them inconsistently, phones mostly do not, and installing an office suite to read one document is a poor trade. Converting to PDF solves it in a few seconds.
How it works
An .odt is a zip archive. Inside it, content.xmlholds the document in OpenDocument's own XML vocabulary — headings are text:h with an outline level, paragraphs are text:p, lists are text:list, tables are table:table. Those map onto the same structures a PDF typesetter needs almost one for one.
So the archive is unzipped in the browser, the XML is parsed with the browser's own parser, and the resulting structure is typeset onto pages. No conversion library, no upload, no server.
What comes across
Kept: headings and their hierarchy, paragraphs, lists including nested ones, and tables.
Not kept: fonts and colours, headers and footers, page numbering, footnotes, text frames, drawings and charts. As everywhere on this site, the output is a clean re-flow of the content rather than a facsimile of the original page.
If exact appearance is what you need and you have LibreOffice available, its own Export as PDF will always beat this, because it is the program that laid the document out.
Common uses
- Reading an .odt on a machine with no office suite installed
- Sending a LibreOffice document to someone who only has Word
- Submitting to a portal that accepts PDF only
- Freezing a document so it cannot be edited in transit
Privacy
The file never leaves your device. Given that the format is standard in government and legal work, that is exactly the property that matters here.