In order to stop the error when Edge opens pdf files please do the following:

1. Click on the 3 dots on the top right hand side of the browser
2. Click on Settings [ Settings Tab Opens ]

3. Once the Settings Tab opens click on the search bar on the top right and type 'pdf'
4. Once you type pdf scroll down on the right hand side until you reach PDF Documents and click on the arrow pointing right.

5. Once the pdf settings open make click on 'Always download PDF files' to make sure pdf files will download instead of opening.
6. Close the Settings Tab
7. Test the website that was giving you the error once more.