Thank you for your answer.

I've tried the solutions of the other thread you've pointed, but still doesn't work.

But I could find something interesting :

As I explained, I copied-pasted text and images from Dreamweaver to MS Word, and I found that if I remove the original images, they don't appear anymore in MS Word.

So it's like Word was keeping the links to thoses images, instead of having really copied the images.

Do you have an idea or do I need to insert again all pictures of the 115 pages ?

Here you can find a sample of my document if needed :
My file

Unfortunately, I think that you are indeed going to have to redo all the pictures in that case - my best advice would be to make sure that the images are all in a folder, then use the Insert > Picture > From file... option - when you have finished entering all the images (boy! that's gonna take some time!!), then I would suggest that you right-click on any of the images and choose Format Picture > Picture (tab) > Compress > All Pictures in Document | Print | tick both boxes in the bottom section.
Hopefully, this will ensure that they are embedded in the document fully (and should reduce the file size and load times).

Ok, I guess I don't have choice.

Anyway, thanks for the help !