Combine data from 2 columns into 1 column

bencredosforkidscom 

If by "Excel document" you mean an "Excel file", you can reference data from one file to another but those files cannot be relocated or renamed once referenced without opening each file, correcting the link(s), and re-saving.

If by "Excel document" you mean "Excel worksheet", this is possible but not by using copy/paste the way you are describing.

1. On the first worksheet select the cells/column that contains the combined data you want copied to the second worksheet
2. On the second worksheet right click the first you want to contain your copied data and under the pop-up "Paste Options" click "Paste Link (N)"

Note how the formula for each cell references the initial worksheet and cell.  Instead of doing a copy/paste you could just as easily have typed the reference formula for the first cell and then use the drag method to insert all the other references you want.