"The Open XML file [name].docx cannot be opened because there are problems with the contents or the file name might contain invalid characters" — or "Word experienced an error trying to open the file" — on a document downloaded from Google Drive or exported from Google Docs

What's actually wrong

Most of the time this is not real corruption. Google Docs' .docx export has quirks Word chokes on (especially documents with tracked changes/suggestions), Windows flags internet downloads so Protected View blocks them, and an interrupted download leaves a truncated file. Occasionally the "docx" is not a docx at all — it's an HTML error page saved under the file's name. A fresh, complete download or re-export fixes the large majority of cases.

Free fixes — try these first

1. Re-export from Google Docs. Open the file in Google Docs (right-click in Drive → Open with → Google Docs), accept or resolve any suggested edits, then File → Download → Microsoft Word (.docx). This regenerates a clean file and is the most common fix.
2. Unblock the download. Right-click the file → Properties → check Unblock → OK. Or open Word first and use File → Open instead of double-clicking; if it opens, Protected View was the problem, not corruption.
3. Check the size and re-download. Compare the downloaded file's size with what Drive shows. If it's much smaller (or a few KB), the download was cut off — re-download on a stable connection, or try a different browser.
4. Peek at the first characters. Open the file in Notepad: if it starts with PK, it's a real docx worth repairing; if it starts with , you downloaded an error page — go back to Drive and download again while signed in.
5. Try a more tolerant opener. LibreOffice Writer and Word for the web both parse slightly malformed docx files that desktop Word rejects; open there, then re-save as .docx.