LibreOffice becomes unresponsive, fills RAM when opening document

I was sent a MS document docx file and I opened it for editing using LibreOffice Writer (LibreOffice 10(Build:2)) on Fedora 24 (x86_64). The problem is it is unresponsive from the beginning, so that I cannot even scroll down the page. Touching the window results in a prompt telling me to “Wait” or choose to “Force Quit”. Interestingly, waiting did not solve the problem, and to my surprise, I faced a grown RAM usage in System Monitor, where LibreOffice was occupying 7.1 GB of my total 8 GB RAM! Soon, the system closed LibreOffice.
While I have never encountered such a thing anytime before, and thinking this might an MS issue, I resorted to converting the file via soffice commandline options as follows to ODT format:

[mhd@localhost sepehri-95]$ soffice --convert-to odt tsunami-fazel-Thu040695.docx  --headless
convert /home/mhd/Dropbox/sepehri/sepehri-95/tsunami-fazel-Thu040695.docx -> /home/mhd/Dropbox/sepehri/sepehri-95/tsunami-fazel-Thu040695.odt using filter : writer8
[1]+  Done                    libreoffice tsunami-fazel-Thu040695.docx

Next, I tried opening the resulting odt file, but the same problem happened for LibreOffice, making it unresponsive and consuming huge RAM.

Any comments on what this is all about and how it can be dealt with?

A new experiment is that running conversion to DOC file type using the following command has the same RAM blowing effect:

[mhd@localhost mm]$ soffice --convert-to doc tsunami-fazel-Thu040695.docx 
convert /mnt/mm/tsunami-fazel-Thu040695.docx -> /mnt/mm/tsunami-fazel-Thu040695.doc using filter : MS Word 97

So, I have to kill the process to save the system from freezing.

You convert a file in Dropbox and save the result directly in Dropbox, right? What happens if you do that on a file on your hard drive?

Right @floris-v, I did not think of it. Let me try the conversion out of Dropbox.

@floris-v conversion out of Dropbox folder did not make a difference on the final result and the problem.

Okay, so it’s really related to that file. You can change the extension to .zip and open the archive, take a look at document.xml in the word folder. Maybe there’s something wrong there.

Please also report the unziped file size (may be is very big), and if this exact file can been opened by someone having MS WORD. Not the original which was uploaded, but the existing in Dropbox. This way you can check if uploading changed or polluted the docx file.