I can't address what you should do to repair Journal other than a reinstallation of the software. Hopefully, someone else can provide additional help for that.
However, regarding what can Journal import, the answer is (practically) everything. It doesn't really do any importing. Instead, it appears to be running some sort of script. The script opens the program that originally created the document you are importing (so you must have the program on your device), then "prints" the document using the Journal Note Writer. All this thing does is to create a picture (Journal format) of the document, save the thing where you tell it, and then open it in Journal.
It is similar to what PDF Writer does to create PDF files if you have ever used that.
I use the import feature for all kind of forms that I have to fill out regularly. Now I just open Journal, fill out the form there, and print it (to paper)! It makes filling out all those organizational forms almost fun!