Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    If True Then
        If openFileDialog1.ShowDialog() = System.Windows.Forms.DialogResult.OK Then
            FolderName = openFileDialog1.FileName

            TextBox1.Text = FolderName
        End If
    End If

End Sub

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click

    If True Then
        Dim fullpath As String = System.IO.Path.GetDirectoryName(FolderName)
        Dim fileExist As Boolean = Directory.EnumerateFiles(fullpath, "*.pdf").Any()

        Dim PdfFile As String = (fullpath & Convert.ToString("D:PDF FILES")) + TextBox2.Text + ".pdf"

        If File.Exists(PdfFile) Then
            System.Diagnostics.Process.Start(PdfFile)
        Else
            MessageBox.Show("File is Not present ")
        End If

    End If

End Sub