It would be a good workaround
if it works, so I would suggest creating a copy of the movie you want to add transitions and/or effects to, and work off that. Doing it that way preserves the original for any errors you make on the way.
The link above shows that WMM will do transitions and effects on photos. Whether they will be good enough for you only you can tell.
I don't know VideoPad at all so I can't say about compatible file, (movie), formats.
But good luck and have a go.