[Compatibility Mode] in the title bar — features greyed out, formatting shifts, document won't save as a normal .docx

What's actually wrong

Compatibility Mode is not corruption — it's Word telling you the file was last saved in an older format flavor, so it disables newer features to keep the file round-trippable with old Word versions. It becomes a real problem in three situations: the Convert command fails or is greyed out, every document (even new ones) opens in Compatibility Mode because your Normal.dotm template is stuck in the old format, or a document that went through crash recovery or a non-Word app keeps reverting to Compatibility Mode with broken layout. The file's content is almost always fully intact.

Free fixes — try these first

1. Convert the document: File → Info → Convert → OK, then save. The banner disappears and all modern features return. Alternatively File → Save As → type Word Document (*.docx) and untick "Maintain compatibility with previous versions of Word".
2. If every document opens this way, fix your defaults: File → Options → Save → set "Save files in this format" to Word Document (*.docx). Then close Word, press Windows+R, run %appdata%\Microsoft\Templates, rename Normal.dotm to Normal.old, and restart Word — a stale or corrupt Normal template is the classic cause of Word "converting all my docs".
3. If Convert is greyed out or fails: start Word in Safe Mode (winword /safe), open the file and try the conversion there; success means an add-in is interfering — disable add-ins via File → Options → Add-ins → COM Add-ins → Go.
4. If the document reverts or misbehaves after converting: select everything except the final paragraph mark (Ctrl+End, then Shift+Click just before the last ¶), copy into a fresh blank document, and save that as .docx — the last paragraph mark carries document-level cruft that keeps old-format flags alive.
5. Expect small layout shifts: after converting, check equations, text boxes and SmartArt — those are the elements Microsoft documents as changing slightly. Use Review → Compare against a copy if precision matters.

If the free fixes fail

Compatibility Mode alone never needs a repair tool — but if converting triggers a contents error, or the file keeps reopening damaged and in Compatibility Mode after a crash or merge, the structure itself is broken, and our free diagnosis will tell you honestly which situation you're in before any repair is offered.