Hello jdip101,
Welcome to Apple Support Communities. It sounds like you're having trouble viewing .png files in the Files app on your iPhone. I'd be happy to share information that may help.
First, take a look at the information here: Use the Files app on your iPhone, iPad, or iPod touch.
Also, check for any available updates for your iPhone: Update your iPhone, iPad, or iPod touch. (Be sure to have a current backup prior to updating.)
Finally, if you're still unable to view .png files in the Files app, please reply with the following details:
-What happens when you try to view the file? Do you receive an error message?
-Have you tried exporting the screenshots as a PDF to see if that makes a difference?
Take care.