Dim Path As String = Application.StartupPath ' "...."
Dim myProcess As System.Diagnostics.Process = New Process
myProcess.StartInfo.FileName = Path & "/document.pdf"
myProcess.Start()
ได้เเล้วค่ะ ขอบคุณค่ะ เปิดจาก Web Brownser เอา Code (VB.NET)
Private Sub Help_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
WebBrowser1.Navigate("C:\Users\Documents\manual.pdf")
End Sub