Identifying Exception Type in a handler Catch Block

I have created custom exception class

public class Web2PDFException : Exception
{
    public Web2PDFException(string message, Exception innerException)
        : base(message, innerException) { ... }
}

In my application how can I find out if it is my custom exception or not?

try {  ...  }

catch (Exception err)
{
//Find exception type here
}