how can we find/search a file at run time from our application with C#?

private bool CheckFileExistance(string filePath)
{
    // it will return true if file is available or false if file is not available
    //use this if your file path will like this.... C:\test.txt
    //filePath = "C:\PDF\test.pdf"   then use this....
    return System.IO.File.Exists(filePath); //path like C:\test.txt
    ///////////////////OR////////////////////////
    //use this if your path is like ~/PDF/test.pdf..
    //so if your pdf files where store in pdf directory then use this method for getting path
    //Server.MapPath("~/PDF/test.pdf")  
    //filePath =   "~/PDF/test.pdf"        then use this....
    return System.IO.File.Exists(Server.MapPath(filePath));
}