I find that copying another filename and trying to substitute the information does not always work.
Instead, try this.
Click on your images tab.
Click on the image of the .pdf you want to link to.
It will come up in the principal editing position (if you know what I mean) so that now, if you click on it again, you will open it.
Highlight and copy the url,
Go back to the profile of the person you're working on.
Then, in edit mode, paste it into the proper place in the "For a larger, clearer version . . . " sentence.
See if that works.