I import an additional MVD using File > Manage Movies > Import.
That is placed under a new tab. I then copy/paste or cut/paste the clips I need to my main movie timeline. When I have what I want, I delete that extra movie.
I find if I export a file as AVI then it drags and drops OK.
Strange MEP accepts AVI and not its own file extention via drag and drop..
I'm surprised to hear that dragging an MVD file to MEP doesn't work for you. It's always been OK for me in all versions right up to my present MEP 2014 Premium, including MX.
BTW, I think perhaps you're confusing project files (MVP and MVD) with video files (MPG, MP4, AVI, WMV, etc). Dragging one of the latter will place the file directly onto your timeline. Dragging an MVD will open a new tab or movie as I said. (Provided that all the links to the various files in that MVD project file have remained intact since it was exported.)
Sounds very unlikely but maybe this is a Windows 10 issue - a serious one. Or possibly you have the basic version of MEP MX and that doesn't allow drag/drop - but there again I'd consider that an unlikely limitation.