In my office I have server with Active Directory and local network. I want to connect web server from another place to this Active Directory. All servers working on Windows server 2008. Office network connect to Internet through PPPoE (router model TP-Link WR-ND941ND) How should I setup router and server to connect my web server to Active Directory from the outside?
If I've understood your question correctly, you have a website (off-site, not on the local network) that you want to be able to use to authenticate against your Active Directory?
If so, you will need some sort of VPN or other such tunnel between the two 'sites'. A site-to-site VPN will give your web server access to your local network for access to AD, once the firewalling etc is setup. So, first step will either be some hardware at each site to support the VPN, or alternatively you can use the RAS service built into Windows Server 2008 to act as the VPN server.
I'm not sure I understand your question exactly. Do you want to authenticate your website users against your Active Directory, or do you want to join your webserver to your domain?
If it is the latter, then you will need to set up a VPN tunnel or some WAN connection as George said.
If it is the former, then you might have some additional options. You may be able to set up Active Directory Federation Services to authenticate your website users against your internal AD without having to set up a VPN tunnel.
Some information on ADFS can be found at the following sites: http://www.dasblonde.net/downloads/ADFSServer2008LabErrata.pdf - WARNING - PDF! http://technet.microsoft.com/en-us/library/dd391937(WS.10).aspx