Send whatsapp message with pdf file in Windows Application

I have written the code to send the Whatsapp message using the windows application using web.whatsapp.com but cannot figure out how to send it with a pdf file.

Please help me with how to send a Whatsapp message with pdf file

below is the code I have done to send the Whatsapp message using web.whatsapp.com

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Try
        System.Diagnostics.Process.Start("http://web.whatsapp.com/send?phone=" & txtto.Text & "&text=" & txtbody.Text.Replace(" ", "+ encodeURIComponent(E:/BGLStock.pdf)") & "")
            Timer1.Start()
    Catch ex As Exception
        Timer1.Stop()
    End Try
End Sub
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
    Dim sec As Integer = 0
    sec += 1
    If sec = 10 Then
        SendKeys.Send("{ENTER}")
        Timer1.Stop()
        sec = 0
    End If
End Sub