You’re unlikely to get step-by-step instructions here, just general pointers.
NDM (now known as Connect:Direct from Sterling Commerce) provides value-added file transfers. Probably the easiest way to interact with NDM from IS is to use FTP. Or simply use data exchange directories where both products drop off and pick up files.
If NDM provides client libraries (the literature implies that they do), you may be able to hook those in to IS to create and expose services to replace the built-in pub.client.ftp services for use by your integrations. If you use Trading Networks, you might be able to create a custom delivery method that uses the client libraries.
HTH
#webMethods#edi#Integration-Server-and-ESB