Obtaining Letter of Support from Colleagues External to University for P&T
You can request the letter but I would recommend that the request be directly sent by and returned to the chair of the department or the chair of the departmental P&amp;T tenure committee. They can then decide if it should be attached to the P&amp;T file.

As far as sharing it via Google Drive or equivalent services, I would suggest that you investigate if your institution has a designated file transfer service and use that instead. Your P&amp;T file is probably not something you would want to have "leaked."