Mobilize doesn't include file editing or collaboration. If you'd like to share files, you can import and export static files in the Files section of each group's Lounge so that your members always have access to important resources from you and community members.
If you need a file collaboration software, check out Google Drive, Quip, Dropbox, Box, Airtable, and Microsoft Office 365. You can always include an embedded URL to those files within your Mobilize post discussing that file.