You can use reference from MDB1 to MDB2, so MDB1 will recognise all the
functions in MDB2.
Open MDB1, when you are in code (any where), select tools, reference. browse
and select MDB2.
You will notice that MDB1 recognise all the functions in the modules, but it
wont recognise forms, reports, macros etc, so if for example you want to open
a form MDB2 From MDB1, create a function in MDB2 that open the form, and then
call that
function from MDB1
That way you wont open another MDB, and it will look like the form is
located in MDB1