...
$odmhandle = AllocMemory( 4 );   # <-- 32 bit DWORD
...
# retrieve and store the handle in $odmhandle
$odmregisterrc = ODMRegisterApp($odmhandle, ...);

# use the value of $odmhandle as 32bit DWORD
ApiLink ('odma32.dll', 'INT ODMSelectDoc(DWORD OdmHandle, ...);
$odmselectrc = ODMSelectDoc($odmhandle,$docid,$flags);