How to share a document between groups
Key point: A single document cannot be shared between groups, rather, the containing folder is shared.

Prerequisites

User must have a role of manager of the parent project to be able to add or remove a shared folder from the group.

From the group sharing page:

  1. Click the Share folder... button at bottom left.
  2. In the Share folder dialog, choose a folder to share to another group:
    1. Click the icon to select the folder from the drop-down list
    2. Or click the icon to select folders in the folders tree
  3. In the Share with... section, in the Group field, start typing the name of the group you want to share to then click the name of the group from the list of autosuggestions.
    1. Click the checkbox to allow members of the selected group to edit the contents of the folder being shared. Note that an administrator can still edit any documents.
    2. To remove the group, click the Remove button . 
  4. If the folder is to be shared to more than one group, start typing the next group name and repeat previous step.
  5. Click the And/or make public checkbox if you want to make the folder being shared available to the public.
  6. Click the Share button to share the folder.

You can modify the sharing details at any time. Click the Edit button on the right of a shared folder to open the Edit share folder dialog and then make changes to the sharing details for the folder.