Dim Ordner As String="C:\Deinordner"
Dim DeinString As String="DeinSuchbegriff"
Dim PfadZumPDFReader As String="C:\Program Files (x86)\Adobe\Acrobat Reader" & _
  "DC\Reader\AcroRd32.exe"
 
For Each fil As String In System.IO.Directory.GetFiles(Ordner)
If fil.Contains(DeinString) Then
Process.Start(PfadZumPDFReader, fil)
End If
Next

EALA FREYA FRESENA