if (sourcePath.Contains(".")) // then treat this path as a file

if (File.Exists(sourcePath))
{
    // then treat this path as a file
}

if(File.Exists(path))
{
    // This path is a file
    ProcessFile(path);
}
else if(Directory.Exists(path))
{
    // This path is a directory
    ProcessDirectory(path);
}
else
{
    Console.WriteLine("{0} is not a valid file or directory.", path);
}

public bool IsFolder(string path)
{
    return ((File.GetAttributes(path) & FileAttributes.Directory) == FileAttributes.Directory);
}

Public Function IsFolder(path As String) As Boolean
    Return ((File.GetAttributes(path) And FileAttributes.Directory) = FileAttributes.Directory)
End Function

Try
    Dim isExistingFolder As Boolean = IsFolder(path)
    Dim isExistingFile = Not isExistingFolder
Catch fnfEx As FileNotFoundException
    '.....
End Try

var isDirectory = (File.GetAttributes(path) & FileAttributes.Directory) == FileAttributes.Directory;

public bool IsFolder(string path)
{
    return ((File.GetAttributes(path) & FileAttributes.Directory) == FileAttributes.Directory);
}

// Define a test path
string filePath = @"C:Test Folder";

if (IsFolder(filePath)){
    MessageBox.Show("The given path is a folder.");
}
else {
    MessageBox.Show("The given path is a file.");
}