Private Sub UserForm_Initialize()
Dim i As Long
Me.ListBox1.Clear
Me.ListBox1.AddItem "File Numbers"
Me.ListBox1.Selected(0) = True
For i = 2 To Sheet1.Range("A10000").End(xlUp).Offset(1, 0).Row - 1
Me.ListBox1.AddItem "File Number" & i + 9999
Me.ListBox1.List(ListBox1.ListCount - 1, 1) = Sheet1.Cells(i, 1).Value
Next i
End Sub

Private Sub CommandButton1_Click()
Dim MyFolder As String, i As Long
MyFolder = Application.GetSaveAsFilename()
Sheet1.Range("A10000").End(xlUp).Offset(1, 0).Value = MyFolder
Me.ListBox1.Clear
Me.ListBox1.AddItem "File Numbers"
Me.ListBox1.Selected(0) = True
For i = 2 To Sheet1.Range("A10000").End(xlUp).Offset(1, 0).Row - 1
Me.ListBox1.AddItem "File Number" & i + 9999
Me.ListBox1.List(ListBox1.ListCount - 1, 1) = Sheet1.Cells(i, 1).Value
Next i
End Sub

Private Sub ListBox1_Click()
On Error Resume Next
Me.AcroPDF1.LoadFile Me.ListBox1.Column(1)
End Sub