There's no simple answer, but you can try a few things. Biggest clue is the close command not being present.
- Make sure you're only selecting 2d lines: Set filter to shapes only.
- Make sure the lines are all on the same layer: With all the 2d lines selcted, in the properties dialog, the layer name is visible. If it's blank, you have more than one layer.
- Probe around: Select one shape at a time, and see what's what.
- See if Join works: Select two adjacent shapes with a common endpoint, then select Join. They should now be one shape. Then try Join with all the 2d lines.
- With all those issues resolved, Close should now work.
- If all else fails, use the dxf lines as a template, and trace over them with a polygon.
I was able to close the geometry, and convert to Board outline.
The key was using the filter "Select Shapes", I was using "CTRL-Left click" to select all the segments.
Thankyou very much. You were more helpfull than Tech support.