I have other base64 values that will render in the viewer, but am not sure why this one isn't. Is there a way to assess why? Here's a copy of what the document looks like (if that helps).
Can you share a clearer image of the config of the pdf viewer (your second image). I'd like to see where you set the base64 value in the component. It's cut off and didn't show where you set the value.
Then, when I access the value from the PDR viewer, it shows the string depicted above. Here are a few shots of what I set the File URL value to be and you can see that the base64 value is showing but not rendering in the component.