The newest version of the NR7-R Application for Refund of Part XIII Withheld is now available on the CRA website.
Payments subject to Part XIII tax are normally passive income where the tax is the final tax (and no Canadian Income Tax Return is required to be filed). The normal Part XIII rate is 25% but is often reduced by treaty.
This form is filled out by the “beneficial owner” of the payments if too much tax has been withheld on payments.