Solution 1:

When I downloaded my VSTO program to a new computer from a github branch and attempted to build the project again I received the error: “Unable to find manifest signing certificate”.

I did some Google searching and found the stack overflow article with the proper solution.

Once I deleted the code lines I was able to build the project.

Solution 2:

Alternatively, you can create a Test Certificate from the Signing tab in the Project Properties since I was also unable to “Select from Store…” to get a signing certificate.