Select this feature from the File menu and choose the Fast-Help Project that you want to import pages from. The Topics and Popups from that Project will be loaded into the following screen:
You can choose another Project if you want to, using the ellipsis button on the right of the Project field. Select the pages you want to import by checking the box beside each one. A little [x] will appear when the page is checked.
Click the [Check All Pages] button to check all pages on the current tab or [Un-check All Pages] to reverse that. You can use the [Expand All] and [Collapse All] buttons to expand and collapse the Contents tree.
The HelpIDs and ContextStrings for the imported pages will not be changed, unless there is a conflict with existing pages. In that case, new ContextStrings and HelpIDs will be automatically assigned.