If file excist else open other one

I am using this to open a file in google docs in a webview

Webview.Source = "https://docs.google.com/document/d/1R_veGr31e39d4gJa0CtAdzU5BxDl5ZV-2bssofU8wSU/edit?usp=sharing";

But when it is not there i want to open another one as backup.
When removing the first from google docs it is not opening the second one

Trying to make a if statement , no luck

` if (File.Exists("https://docs.google.com/document/d/1R_veGr31e39d4gJa0CtAdzU5BxDl5ZV-2bssofU8wSU/edit?usp=sharing"))
{
Webview.Source = "https://docs.google.com/document/d/1R_veGr31e39d4gJa0CtAdzU5BxDl5ZV-2bssofU8wSU/edit?usp=sharing";

            }
          else
            Webview.Source = "https://docs.google.com/document/d/1JtPBbacWjjE1RnqT7MlliexLFk618iNS5yUBBCkh1bs/edit?usp=sharing";
        {

            }
    }`