I'd like to be able to view the full path of a file, rather than just its file name, in document-based apps like Preview & TextEdit. Is this possible?
Not in a copy/pasteable format, but if you right-click the file name in TextEdit or Preview, it will show the path as a graphical hierarchy.
Copy/pasteable would be Get Info on the file from the Finder, I guess. Depending on the target application you can also just drag the icon from the application, e.g. into Terminal.