Hello Konstantinos,
Welcome to Microsoft Community.
To resolve the issue let us follow these steps:
You may check if the issue resolves while viewing the document in the Word Safe Mode.
To open Word 2013 in the Safe Mode please follow the steps as shown on the following Microsoft Resource article.
Note - The above article lists steps for all Microsoft Office 2013 applications, however, follow the steps to open Word 2013 in the Safe Mode.
The above step opens Word in the Safe Mode. Check if you are able to view all text in the document normally in Word Print Layout view. If yes, then you may follow the next set of steps in the above mentioned article to troubleshoot Add-Ins in Word.
Try the above steps and let us know the result.
Hope the above information helps.
Thank you.