in reply to How can I open a file in it's default program ?

I think you can simply do

system(qq{"$path_to_document"})

If not, you can definitely do

system(qq{start "" "$path_to_document"})

Update: I answered about subject question, default program. The program used to originally create the file could very well be an entirely different. I didn't notice that the question in the body of the post was different.