Here is where I am at now.
Command: (vl-file-copy "//GES-FS-01/design Support/CAD/Acad Blocks/GUY BLOCKS/XXX-ODOT-BLOCK.dwg" (getvar "DWGPREFIX")(subsrt(getvar "DWGNAME") 1 4) "-ODOT-BLOCK.dwg") ; error: no function definition: SUBSRT
Not a programmer, so this "no function definition" doesn't really tell me anything. I'm very close though. To recap, this is the goal - Open a base drawing from the project folder (so the code has something to work with) execute the custom button to copy the XXX-ODOT-BLOCK.dwg from the static support folder and derive the destination folder & project # from the previously opened 1084-BASE.dwg resulting in the XXX-ODOT-BLOCK drawing being copied to the project folder and renamed 1084-ODOT-BLOCK.dwg. The base drawings will always have the 4-digit project# as a prefix to the file name.