A family of Microsoft word processing software products for creating web, email, and print documents.
Try recreating it in a new document in Word 2007. Create a new blank file. Select the whole document, EXCEPT for the very last paragraph mark. Paste into the new blank file, save it as DOCX. When you subsequently open it in 2010, DO NOT convert to 2010 format. Keep it in 2007 format. I am suggesting 2007 format because it is the lowest common denominator. No features have to be degraded when opening the file.
If that doesn't work, try save as to RTF format. That will keep much (but NOT ALL) of the formatting. Then Save As back to 2007 DOCX format.
Also stop switching between 2010 and 2007. Pick one and stick with it. Normally you can switch between the 2 versions with minimal impact. But apparently there is something specific about your document that cannot handle the repeated conversions.
Given the OP uses Word 2010, which does display all the content, using Word 2007 for the repair when it has problems displaying all the content is dumb advice. Likewise, copying all except the last (accessible) paragraph mark in Word 2007 is pretty useless if the content after that is inaccessible.
Your contention "no features have to be downgraded" by using the Word 2007 format is nonsense. Word 2010 makes numerous extra features available when working in its native mode that are not preserved in the Word 2007 format.
Furthermore, switching between versions is of no consequence if the document is in the earlier version's format. Only if the OP needs the features Word gives by working in Word 2010's native mode will working on the document in Word 2007 will have to stop.