Ciao Alessio,
One option is to upload the review form document to the Publisher Library in the Workflow Settings. This will then supply a URL that you can place in your reviewer guidelines for reviewers to access and download the file. They will need to save the edited file and then upload it when they complete their review.
Have you also tried converting the Word file to a Review form in OJS? This is available under Workflow Settings > Review > Review Forms. Any information placed in the Reviewer Guidance field will also be available with the review form.
Un caro saluto,
Kate