For me, delving into XML files with notepad++ is still a black art, and I am not always successful. I really only know enough to be dangerous. But then, nothing ventured, nothing gained.
In the case of your file, when attempting to open it in Word, the details of the first error message

are not very helpful, but when you click on OK, the following dialog appears

and if you click on the Yes button, another error message with Details button on it appears and clicking on the Details button, this time we see

which tells us that there is a problem in the document.xml file at line 2 column2698443
So, when we have changed the file extension to .zip and have extracted the files from the archive and opened the document.xml file in Notepad++, we use the search facility to find that position in the file

In the above screen shot, the purple shading result from the selection of the tabs with the darker purple being the actual position in the file that is selected being Line: 2, Column 2698443.
Notice that because I have selected the closing tag, the corresponding opening tag at the top of the screen shot is also selected.
Now immediately to the left of the closing tag, there is another tag </w:pict> When I move the selection to the left to Column 2698437, the whole of that tag becomes shaded,

but there is no matching opening tag within the <w:p w:rsidR="001B1535" w:rsidRPr="00644965" w:rsidRDefault="001B1535" w:rsidP="00644965">....</w:p> opening and closing tags. Something else that is strange about this tag is, that while it does get selected
as a tag, the "/" seems to be misplaced as it is at the end, instead of at before the w:.
My suspicion about this "tag" is confirmed by searching for other instances of w:pict, which I find further down the file

and not only this time is the / before the w: but there is also a corresponding opening tag <w:pict>
So, here's where I start making rash decisions and first I delete the <w:pict/> "tag" and the re-archive the files and rename and then try to open it Word, without success, this time telling me that the problem is at column 2698434, which is the original
problem tag that has had its position in the file changed because of the deletion of the <w:pict/> "tag"
So at this point, I make another rash decision and delete the whole <w:p w:rsidR="001B1535" w:rsidRPr="00644965" w:rsidRDefault="001B1535" w:rsidP="00644965"> and </w:p> tags and everything in between them.
After doing that, and then re-archiving the files and then re-naming them, I was able to open the file in Word.