Creating a valid Border Layer that FAB3000 can use for various commands (like Panelize, Realistic PCB Viewer, DFM Checks, and more), is probably the second most import step after importing your design.
FAB3000 - 3 Requirements for a Valid PCB border:
We've created a command to attempt to automatically generate a valid Border layer called: Detect PCB Border (Auto). To detect and create a board outline, use the command menu: Fabrication | Detect PCB Border (Auto)..
Note: Since there is no border in the sample gerber file (just polygons), FAB automatically uses the extents of the given design to create the border (if more gerber layers are available, than FAB would detect the actual PCB border).
To add X & Y dimensions (menu: Add | Dimension) or if you have the entire design loaded (including drills) use the command menu: Fabrication | Create FAB Drawing... Here's a quick video showing me add various dimensions, https://numericalsoftware-update.s3.amazonaws.com/tutorials/2022-10-31_13-47-12_dimension.mp4