I am using JCE version 2.8.18. When I go to insert a link to a PDF file (without having any text selected in the editor), after I select the file and click Insert, I am not able to type anything in the Text field. It has the words "Element Selection" greyed out - inspecting this field is says it's disabled. (see attached screen shots).
I checked on another site using version 2.8.14 and it does not have this issue.