The new document generated after comparing and reviewing two Word documents cannot be saved or saved as a copy.

Hi Wuyuan,

It seems to be a Word feature limitation in terms of saving auto generated compared file, however there is a workaround that you may try, but before that, let me share to you an overview on what is happening

When you use Review → Compare in Word, the resulting comparison document is sometimes created as a temporary, in-memory document rather than a fully instantiated file. Internally, Word treats it as a dynamically generated view that references the two source documents. In that state, Word may allow you to review changes but does not immediately commit the document to disk, which is why saving can fail or produce a blank file.

This behavior most commonly occurs under these conditions: • The comparison was launched from within an already-open document rather than from a blank Word instance • One or both source files are stored in OneDrive, SharePoint, or another synced location • AutoSave is enabled and Word attempts to reconcile the temporary compare document with cloud storage • The documents are protected, read-only, or opened from email/preview • Word is running in the newer comparison engine (Microsoft 365 / newer perpetual builds)

That is also why you cannot tell “where it is stored” — it actually is not stored anywhere until Word successfully materializes it as a file.

To reliably save a comparison document, the following approach is the most effective and avoids the blank-file issue:

Open Word without opening any document first, then go to Review → Compare → Compare. Select the original and revised files, and in the “Show changes” option choose “New document.” Once the comparison opens, immediately go to File → Save As and save it to a local folder (e.g., Documents), not OneDrive. After it is saved successfully once, you can move it elsewhere.

If the document still refuses to save or saves blank, use File → Save a Copy instead of Save As, then close Word completely and reopen the saved copy. This forces Word to write the comparison content to disk instead of regenerating it dynamically.

If you already have a comparison open that cannot be saved, you can recover the content by copying everything from the comparison document (Ctrl+A → Ctrl+C), opening a new blank Word document, pasting the content, and then saving that new document. This works because the pasted content is no longer tied to the temporary comparison object.

To prevent this going forward, it is also advisable to temporarily disable AutoSave while performing comparisons, ensure neither source document is read-only or protected, and avoid comparing files directly from cloud-synced folders during the initial save.

So in short: yes, what you are seeing can be normal for Word’s compare engine, but it is a design limitation rather than expected user behavior. The workaround is to explicitly force Word to create a new document and save it locally before continuing work.