Installing owncloud on server 2012 r2

hello everyone
I know that installing on windows server 2012 r2 is not supported, I have a domain all our servers are windows I don't know if installing owncloud on linux will allow the users in windows domain access own cloud with their existing accounts I don't need to create a new users for them is it possible or I have to search for alternative software that support integration with Active Directory

Best

You can configure an ownCloud installation running on Linux to use your AD to authenticate your users. This is explained here:

https://doc.owncloud.org/server/latest/admin_manual/configuration_user/user_auth_ldap.html

thanks for your clarification. but if I went for ubuntu should I install it in ubuntu desktop or server ?

The choose of the used linux distro is up to you. There should be some webpages / wikis out there explaining you the differences between ubuntu desktop or server.

Desktop version often already include a GUI which is not needed on a server. If you don't want to update your Ubuntu system very often, rather go for the LTS version.