Try also to restore the file using this online service. I found it in Google. https://onlinefilerepair.com/en/rtf-repair-online.html
Whatever you'll try to do, make sure you have a proper backup to avoid additional file damage.
In the extreme case, if these suggestions do not help, then you have the ability to restore documents by using Word Recovery Toolbox. I think it will probably help you. http://www.oemailrecovery.com/word_recovery.html