How to configure access to documents?

Question

VPN

Good afternoon.
There are 2 organizations, 2 different offices, 2 different domains.
An employee works in one office, but often collaborates with a second organization. Transferring files via email. Apparently he was not comfortable. Wants that he had access to file spheres in the 2nd organization. You can make a tunnel, but how will the user have access to another domain? Do you need to create domain trust relationships?
1st organization windows server 2012.
2nd organization windows server 2003.
I would be very grateful for any advice. Thank you.

Answer 1

Trust relationships between domains. And add a user of another domain to the group of the first one to manage the rights to the desired resource (they will have an icon with a red plus).