Yes,
in main program, use:
#include "whatever.dba"
e.g.
main proggy:
#include "sub.dba"
gosub setup
print a
wait key
sub.dba
Also, click 'Files' in editor, and browse or add new .dba files. They then get listed in that drop-down selector at top of editor for easy editing of multiple files at once.
There are some complicated rules about multi-file projects but I don't know what they are. Mostly about arrays and global variables.
All of this is only important of course if you are running DBPro!
The programmer formerly known as sonic