Your question makes me think that you might confuse video files and project files.
you start with a video file to
input that into the media room, and then I assume you move this file to tHe timeline for editing work?
If you are done editing, it is good to
save the editing work by saving it as a project. Once you have saved the project, you can
open the project again, e.g. next day after you have opened PD. All the editing into the time line you did before saving the project, is available again upon the
opening of the project.
Mind you, the original video file is still untouched, nothing has change in there, PD has kept your editing activities separately and stores all those typically in the project file.
Only after you have
produced a new video file, using PD production you have (in a new file) the result of all your editing. THIS video file can be shared with others e.g. on DVD or online, or .... as I assume you may be doing.... for the next editing you still may want to do on the video. In that case the new produced video file is again IMPORTED into the media room, and moved to the timeline lie for editing, likely after you have started a new project or have cleared the timeline as required.....
so the project file with all the savings is only for the next time you want to edit the project. It contains editing instructions that only PD understands. Distributing the project file (.PDS) does not make sense to the happy viewer of your editing results.
Hope that the difference between importing a clip and opening a project file is clear and helps you as an answer to your question?
Suggest that have a look at the many tutorials on Powerdirector on YouTube, which may strengthen the explanation above. There are some very good tutors out there!!