Archivos con extensión específica

Dim ext() As String = {".txt", ".XML"}
Dim dinfo As DirectoryInfo = New DirectoryInfo("C:\carpeta")
Dim xfiles() As FileInfo = dinfo.GetFiles.Where(Function(f) ext.Contains(f.Extension.ToLower)).ToArray

Ejemplo1:

Dim files() As String = Directory.GetFiles("C:\carpeta").Where(Function(f) f.EndsWith(".txt")).ToArray

Ejemplo2:
Dim xfiles() As FileInfo = New DirectoryInfo("C:\carpeta").GetFiles.Where(Function(f) Regex.IsMatch(f.Name, "\.(txt|mp3|xml)$")).ToArray


fuente
fuente2

Obtener el nombre del último directorio

For Each d As String In empresas
Dim dname As String = New DirectoryInfo(d).Name
Next


Dim dirfolder As String = "D:\bin\Debug\empresas\789-K"
Dim namefolder As String = Path.GetFileName(dirfolder)