You need to sign your installer and app executable using a certificate. You can get such cert. from many companies, just Google for it. It costs between 100-400 US dollars, certificate is usually valid for a few years (1-3).
Once you have the certificate, you can sign any exe with:signtool.exe sign /t http://timestamp.digicert.com /f yourCertFile.pfx app.exe
And then verify the signature with:signtool.exe verify /pa /v app.exe
The signtool.exe is part of Windows SDK, which you can get from Microsoft, free of charge.