Are you experiencing display artefacts? Suppose the original .docx has been written on a computer in dark mode and user has somehow forced text colour to white. If your computer is light mode, background colour becomes white but forced colour text remains white. Then, “blank” document!
As a check, enable View
>Formatting Marks
. If you see pilcrows (mirrored P hinting at paragraph marks), centred dots (for spaces) or small arrows (for tabs), converted document is not empty at all but direct formatting is playing tricks on your back.
Try to select all text, then Format
>Character
, Font Effects
tab and set Font color: to Automatic.
Does it improve the case?
If you need more help, please mention OS name and LO version. We already know document is DOCX.
EDIT
(You shouldn’t have clicked on “Suggest a solution” but on the Comment call out below my own comment because you don’t provide a solution.)
What is the file size? If it is not confidential or private, can you attach it to a comment (file size limit on the order of 1MB)?
EDIT 2
Change the file extension from .docx to .zip and open it with a ZIP utility. If the file structure is not corrupted you should see a collection of directories and files. Extract the “contents” file (likely named contents.xml) and try to open it with a text editor. It should show the text with formatting mark up.
It is not manageable under this form but this will rule out a certain number of hypotheses.
I also suggest you ask the author for a txt version. Of course, all formatting will be lost, but if you have a deadline, you can start working on the document.