Hi,
For User 1, you can create a Share from SAP Mobile Documents. (e.g open Web Client and go to Share tab and create share there. You can do this from mobile clients too)
Now, select the Share and choose action "Manage Share" and add the User 2 as either Administrator, Contributor or Reader.
Now, User 2 can view this share in his Shared tab.
Collaborate with your colleagues using SAP Mobile Documents
Regards, Ashwani Kr Sharma