C#, FolderBrowserDialog show files in a folder and select a file

FolderBrowserDialog is purely ment for Selecting folders ofcourse.

You are looking for OpenFileDialog.

A little example:

OpenFileDialog openFileDialog = new OpenFileDialog();
openFileDialog.Filter = "PDF Files|*.pdf";

if (openFileDialog.ShowDialog() == DialogResult.OK)
{
   string filePath = openFileDialog.FileName;
}

the filepath string now contains the full path to the file you have selected and you can let your own code loose upon it :)

Good luck!