打开.pdf文件而不是打开文件的功能

Question

我创建了以下函数来从winform上的按钮打开.pdf文件：

Function OpenReports(fileName As String) As String
  Dim xlWBPath As String

  Try
    xlWBPath = Globals.ThisWorkbook.Application.ActiveWorkbook.Path
    System.Diagnostics.Process.Start(xlWBPath & "\fileName")
  Catch ex As Exception
    MsgBox("The " & fileName & "is not found on directory")
  End Try
  Return ""
End Function

当我在这里调用函数时：

Private Sub btnRptEmployeePayToMarket_Click(sender As Object,
                          e As EventArgs) Handles btnRptEmployeePayToMarket.Click
  OpenReports("Ranges to Market.pdf")
End Sub

进入错误陷阱。它无法找到该文件。但是，如果不是运行该函数，而是将其作为Private Sub执行，如下所示：

Private Sub btnRptEmployeePayToMarket_Click(sender As Object, e As EventArgs) Handles btnRptEmployeePayToMarket.Click
  Dim xlWBPath As String
  Try
    xlWBPath = Globals.ThisWorkbook.Application.ActiveWorkbook.Path
    System.Diagnostics.Process.Start(xlWBPath & "\Ranges to Market.pdf")
  Catch ex As Exception
    MsgBox("The file Ranges to Market.pdf is not found on directory")
  End Try
End Sub

然后它工作正常。所以我认为它与我的功能有关，但我无法弄清楚它是什么。