I use Win 7, Version 7.0.1.2 LibreOffice
I am saving documents in .docx format
But when I send such a document to someone who uses MacOS (current version), they cannot open the file.
The other user is using Pages.
Please advise,
Thank you!
David
Mac users cannot open .docx documents created by LibreOffice
Does the mention of LibreOffice in your title imply that the other user can open .docx created by any other application (e.g. MS Word)?
I am going to double-check on this (I will have several Mac users open a .docx file created from MS Word, and then .docx file created from LO). I believe it is the case that they can open the .docx from MS Word and NOT from LO, because I did not have this problem before (with MS Word .docx files) they opened in the past.
Ok,
so you can try opening the docx with an offical docx viewer form microsoft. For example:
Get Doc Viewer - Microsoft Store
If that works and displays as you would expect, you can be at least sure that it’s a problem with Pages and not with the LO Export.
Hope that helps.
Sorry. I did not make clear. The other user has only Mac’s built in word processor - Pages. They do not have LO.
There is an easy solution for that: 
https://www.libreoffice.org/download/download/?type=mac-x86_64&version=7.0.1&lang=en-US
+1 for igorlius suggestion. And then use ODT files.
You could open a bug report, but I’m not optimistic that someone will try to to fix this, unless you can prove, that the file from LO also fails for MS Word.
The utility above is for Windows. This issue is faced by those using MacOS, so it would not apply, but thank you anyway.
@David108, I was suggesting, that you would doublecheck the document with the Viewer, since you are under Win 7. Just to clarify.
Resolved! It turns out that in the Options, I had selected OpenOffice .docx rather than MS Word .docx
Now it is obvious that even though the extension is the same, there are differences.
Please take care - the format is called: Office Open XML Text (Transitional) (.docx), which got nothing to do with OpenOffice (I admit, that this is really confusing nomenclature) - see Office Open XML.