Eventually I used the code from SoMad but adjusted it a little bit ;) Still loads of thanks man :D
private void Dutch_Click(object sender, EventArgs e)
{
string[] Filelistarray = Directory.GetFiles(@"C:\Users\a961835\Programming", "*.txt");
DataTable dt = new DataTable();
dt.Columns.Add("FileName");
foreach (string FileName in Filelistarray)
{
DataRow dr = dt.NewRow();
string filenameWithoutPath = Path.GetFileName(FileName);
dr["FileName"] = filenameWithoutPath;
dt.Rows.Add(dr);
}
DropDownList.DataSource = dt;
DropDownList.DisplayMember = "FileName";
}