yes, you can add a pdf file if you want. When the files browser is opened, choose to see "All files", instead of just "Images files". Then choose the file you want, and click OK. The file will be added to the event you want.
Once done, you won't be able to open it from the "internal" viewer, but a right click on it from the gedcom editor for example, will open it without any problem.
Something you must know: this editor you use, the Extended Editor which is the default editorn will be replaced by the "simple editor" which is almost completed. It will be the default editor when 0.9 is released.
If you have requests about it, feel free to post them in the mailing list, it's faster. Francois