“We can't open … because we found a problem with its contents”

Word says “We're sorry. We can't open Report.docx because we found a problem with its contents.” Older versions say “The Office Open XML file Report.docx cannot be opened because there are problems with the contents.” Both mean the same thing, and the Details button tells you a lot about how bad it is.

Read the Details first

Click Details in the message. You'll usually see one of these:

“The file is corrupt and cannot be opened.” Word couldn't even unpack the file. Typical of a save or copy that was cut short, or a file with zeros written over part of it.
“Unspecified error” or a line like “The name in the end tag of the element must match the element type in the start tag”, followed by Location: Part: /word/document.xml, Line: 2, Column: 48211. Word unpacked the file fine, but the text inside isn't laid out correctly at that point. This is often very recoverable.
“Illegal XML character”. A character Word's format doesn't allow got into the text, usually from a paste or from software that created the document.

The Part tells you which piece of the document is damaged. A .docx is a zip folder of small files: /word/document.xml is your main text, /word/footnotes.xml the footnotes, /word/header1.xml a header, and so on. If the part isn't document.xml, your main text is probably fine. Ignore the line number: the whole file is usually one long line, so only the column matters.

What usually causes it

The document was saved while the computer crashed or went flat, or a USB stick was pulled out.
OneDrive, Dropbox or an email attachment delivered an incomplete copy.
A program that creates Word documents (reporting tools, document generators, translation tools) wrote something Word doesn't accept.
Older Word versions had bugs with equations and text boxes that produced exactly the “end tag” error.

Free things to try first

Make a copy and work on that.
If Word asks whether to recover the contents, click Yes.
File → Open → Browse, select the file, click the arrow next to Open and choose Open and Repair.
Open it in LibreOffice Writer (free) or Google Docs. Both are more forgiving with small errors in the text.
Look for an earlier version: right-click → Properties → Previous Versions, or version history in OneDrive or SharePoint.
If you're comfortable with it: copy the file, rename the copy from .docx to .zip, open word/document.xml in a text editor, go to the column from the Details, and fix the broken tag. This works for one small error, but it's fiddly, and one wrong edit makes it worse.

Where Office File Repair helps

Office File Repair does the fiddly part for you. It unpacks the file even when the zip is cut short or damaged, then repairs the text around the error: broken tags are closed properly, illegal characters are removed, and text after the damage is kept where it can be read. Parts that can't be saved, such as a broken header or a damaged picture, are left out so the rest of the document opens.

You see a preview of your recovered text before paying anything, and nothing is uploaded: it all runs in your browser.

When nothing can help

If the Details say the file is corrupt and the file is 0 KB, or every byte is zero, there's no text left in it to recover (see file shows 0 KB). Text that was cut off the end of a file is also gone for good: any tool, including ours, can only recover what's physically still there.

Common questions

What does “Part: /word/document.xml, Line: 2, Column” mean in a Word error?

It points to the place Word stopped reading. /word/document.xml is the main text of the document, and the column is the position of the error inside it. The line number is almost always 1 or 2 because the whole part is stored as one long line.

Is “The Office Open XML file cannot be opened” the same error?

Yes. That's how Word 2007 and 2010 word it. Newer versions say “We're sorry. We can't open … because we found a problem with its contents.” The causes and fixes are the same.

Will Open and Repair fix it?

Often, when the problem is one small error in the text. It usually fails when the file was cut short or overwritten with zeros, because Word can't unpack the file in the first place.

Can I open the document in something other than Word?

Yes. LibreOffice Writer and Google Docs are free and sometimes open documents that Word rejects. Save a copy as .docx from there once it opens.

Check your document: the preview is free