As Ronald mentioned, Its not possible to open the .mda file with your modeler.
You need .mpk file.
- if you have exported your entire project you get .mpk file which you can open with modeler
mda is kind of like a built or compiled version of your project.
You can not download a package and try to open it. You need to open your modeler and open the project from there. If it is not on your local disk it will download from the teamserver if you have the rights and the project uses the teamserver offcourse. If you want to create a package that can be opened by the modeler you should use the export function from within the modeler.