Can I add Bitcoins by address? I signed up for bitcoin ages ago, but never used it; I forget who I signed up with I have had to reinstall the OS (Win 10) on my computer and lost the program I used. I do still have a copy of the address though. How do I add the address to MultiBit?
Edit: I apologize I was for some reason still thinking MultiBit classic, if you are using HD there is a possiblity you created seed words which you would be able to restore from.

Information is per: https://multibit.org/try-multibit-hd.html

Classic:
You're going to need the backup wallet or private keys that were automatically created for you by MultiBit. By default they would have been located in a sub-directory of the folder your original MultiBit wallet was created in.

This information is per: https://multibit.org/en/help/v0.5/help_walletBackups.html

If you do not have any of these files/private keys you are out of luck with regards to recovering the funds. The wallet address alone will only allow you to view the funds, there is no way to recover funds with a bitcoin address alone.