How do I speed up searching through files on a network drive and prevent "not responding" in VB.Net - vb.net

Question

Part of my application searches for a string provided by a textbox within .txt files and .pdf files stored on a network drive. It works great on my PC when looking within a directory of a few files stored on a local disk, when I run it on my work PC which is less beefy and looking at a network drive I get "not responding" and it takes a good few minutes to finally wake up again. This is only searching through around 100 files and that number is only going to get bigger.
I thought about adding a progress bar, but if the application is not responding I assume the progress bar will not update? I would be very grateful to hear the advice of someone much more experienced in this than me.
In short, the code searches as described above, uses the name of the folder (that begins with SCC) to add an item to a listbox. If it cannot search the PDF for any reason then it adds it to another listbox displaying the folder names it was unable to search.
Here is the section of code that does the search:
Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
Dim path As String = ""
Dim list As System.Collections.ObjectModel.ReadOnlyCollection(Of String)
Dim raf As itextsharp.text.pdf.RandomAccessFileOrArray = Nothing
Dim reader As itextsharp.text.pdf.PdfReader = Nothing
Dim searchPhrase As String = faultSearch.Text
VINListBox.Items.Clear()
Region "search plain text"
'finds text within faultSearch textbox within the files in directory
list = My.Computer.FileSystem.FindInFiles(archive_dir, faultSearch.Text, True, FileIO.SearchOption.SearchAllSubDirectories)
For Each foundFile As String In list
path = foundFile
GetVinName(path)
Next
End Region
Region "search PDF"
'Finds text within faultSearch textbox within PDF files in directory
For Each file As String In My.Computer.FileSystem.GetFiles(archive_dir, FileIO.SearchOption.SearchAllSubDirectories)
If System.IO.Path.GetExtension(file).ToUpper = ".PDF" Then
Try
raf = New itextsharp.text.pdf.RandomAccessFileOrArray(file)
reader = New itextsharp.text.pdf.PdfReader(raf, Nothing)
For i As Integer = 1 To reader.NumberOfPages()
Dim pageText As String = itextsharp.text.pdf.parser.PdfTextExtractor.GetTextFromPage(reader, i)
If pageText.ToUpper.Contains(searchPhrase) Then
GetVinName(file)
End If
Next
Catch ex As Exception
GetErrVinName(file)
End Try
End If
Next
End Sub
End Region
Private Sub GetVinName(ByVal strVIN As String)
Dim fldName() As String
fldName = Split(strVIN.ToString, "\",, CompareMethod.Text)
For x = 0 To UBound(fldName) - 1
If InStr(fldName(x), "SCC", CompareMethod.Text) > 0 Then
strVIN = Trim(fldName(x))
If errListBox.Items.Contains(strVIN) = True Then
errListBox.Items.Remove(strVIN)
End If
If VINListBox.Items.Contains(strVIN) = False Then
VINListBox.Items.Add(strVIN)
End If
Exit For
End If
Next
End Sub
Private Sub GetErrVinName(ByVal strVIN As String)
Dim fldName() As String
fldName = Split(strVIN.ToString, "\",, CompareMethod.Text)
For x = 0 To UBound(fldName) - 1
If InStr(fldName(x), "SCC", CompareMethod.Text) > 0 Then
strVIN = Trim(fldName(x))
If VINListBox.Items.Contains(strVIN) = False Then
If errListBox.Items.Contains(strVIN) = False Then
errListBox.Items.Add(strVIN)
Else
Exit Sub
End If
Else
Exit Sub
End If
Exit For
End If
Next
End Sub