Will the person I send it to be able to open it?

Yes. The editor writes a standard Office Open XML package — the same .docx Word itself writes — with styles, numbering, headers, footers, notes and comments in the parts Word looks for. Word, LibreOffice, Google Docs and Pages all open it.

Does my document get uploaded anywhere?

No. The file is read, edited and written inside the browser tab, and the heavy parsing runs in a Web Worker on the same machine. Open DevTools, go to the Network tab, clear it and open a document: no request carries your bytes.

What does not survive the round trip?

Anything the editor cannot represent is counted rather than dropped quietly: the notes sheet on open and the compatibility check before a save both name it. The usual entries are VBA macros, ActiveX controls, SmartArt and embedded OLE objects, which are stated exclusions rather than bugs.

Can it open a .doc from Word 97?

No, and it says so rather than failing in the zip reader. The old binary .doc is a different, undocumented format; open it once in Word or LibreOffice and save it as .docx, after which everything here applies.

Is there a limit on pages or file size?

No page limit and no tier. The practical ceiling is your device's memory, which is why very large documents are slower on a phone than on a laptop — the same file, the same code, less room to work in.

Edit a Word Document Without Microsoft Word

Open a .docx, change it, and save a file Word still opens — in a browser tab, with no account and no upload. What carries over, and what to check before you send it.