With DEX you can produce 3 different types of work in different file types.
A project is a self-contained file that contains all the schematics, text documents and the PCB to make a PCB. It relies on no other file. Project files have the file extension .project
A project consists of one or more schematics that define the abstract logical design. A project also contains a single PCB which defines the physical Printed Circuit Board that you are designing.
A part is a self-contained file that contains all the symbols and the footprint/land pattern for a part. Like a project file, it relies on no other file. Part files have the file extension .part
A part is an electronic device that you will add to a project to construct your design.
An artwork is yet another self-contained file. This only contains graphics or artwork that you can include in projects and parts by dragging them from the library, Windows File Explorer or the desktop onto a design sheet. Artwork files have the file extension .artwork
When DEX is installed the following file extensions are associated with DEX and Windows will open then with DEX unless you specify another file. To change the file association for a file right-click on the file name and select 'Open With...'