The Open Mode option is used to specify whether projects are to be opened with read or update access. When a project is opened with read access, you may modify a working copy of the project data, but you are unable to save those changes when the project is closed (although you can use the Save As feature to save the modified project as a different project).
When a project is opened with update access, no other Projman session can open that same project with update access; however, read access is available. It is necessary to use update access if you want to save changes to the current project.
For different users to have simultaneous read access to the same project, SAS/SHARE software is required. Note that only one user can have update access to a particular project at a particular time. Access level does not affect the ability to produce project reports.