Search Files on hardrive

I am using this code to get files, but I can not get it to search for all files on C: drive.
How can I get it to show all files Like *.pdf of the drive in the list box

Code:

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Imports System.IO
Imports System
Imports System.Drawing
Imports System.Windows.Forms
 
Public Class SearchAvi
 
    Private Sub BtnGetAviFiles_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnGetAviFiles.Click
 
        Dim dir1 As New IO.DirectoryInfo("c:")
        Dim dir2 As IO.FileInfo() = dir1.GetFiles()
        Dim files1 As IO.FileInfo
 
        For Each files1 In dir2
            FrmListBox.Items.Add(files1)
        Next
 
    End Sub

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Have a look at the help file for DirectoryInfo.GetFiles, it has options you can use for filter and folder selection.