You are able to attach files to a Group record. You do this via the 'Documents' area.
When you click on 'Documents' it will bring up a list of correspondence along with an area where you can 'Attach a file.' Within this section, it tells you to either drag the file or click to navigate to a folder and then upload.
Once you upload a file it appears in the document history. For example I uploaded a word document called Consent Form. You also have the option to View, Rename or Delete the document.
When I click 'View', it downloads the file allowing me to open it.
The list of accepted file types are as follows: