Just in case there is some confusion on file types...
A .vpj file is data; it tells VP how to set up and run a project. The vpj is created from within Videopad with FILE menu|SAVE, FILE|SAVE AS or FILE|SAVE AS PORTABLE PROJECT. These files cannot be loaded into Videopad, nor will they play with a media player. Clicking on a .vpj will open its project in VP, for further editing.
On the other hand, EXPORT|VIDEO FILE is used to save a partial or complete VP project in one of many common video formats or containers: Mp4, FLV, AVI, MOV, etc. These are playable with compatible media players and can be loaded into VP's media area and timeline, as clips. A project cannot be reconstructed from a Video file, as it can with a .vpj data file.