If you don’t have Autocad, or one of the many clones, You will need an App like edrawings, available here
to view the files. There are many others similar .dxf file readers on the web.
If you want to edit or print, a cheap App is Qcad, $39 USD.
Note: You will likely need to download the .dxf files to open them. I don’t think google will open them directly like it does for the excel files.