sorry Charles, but my files were NOT corrupt !
I launched them on another computer and they open normally and allow working on them !
So I guessed that the Word 2019 on my laptop was corrupt !
I tried to uninstall it completely following MS instructions but a reinstallation gave me same issue !
Finally I removed it again, deleted some registry lines regarding office, and reinstalled it...
and now it is working again !!!... and I am a happy man!

Thanks a lot for your assistance.

- a last question please:
the final size of the docx file is 86Mo (353 pages); what is the best way to convert it to a printer-ready PDF-file ? use the incorporated option 'save as PDF' or better not ??