To keep your review/track changes in the new document do the following.
- Save a copy of the Word document. [This is your backup]
- Select the text you want to copy.
- Press CTRL + F3. This will cut the text along with track changes. [Hence the need to follow step 1 and make a backup of the original Word document].
- Open a new Word document.
- Press CTRL + SHIFT + F3. This will paste your selected text AND your reviews/track changes along with it.