Option Explicit

Private Sub CommandButton1_Click()
    Me.Hide
    Me.Tag = 1
End Sub

Private Sub CommandButton2_Click()
    Me.Hide
    Me.Tag = 0
End Sub

Option Explicit

Sub AttachPDFs()
Dim olItem As Outlook.MailItem
Dim olAttachments As Outlook.Attachments
Dim strPath As String
Dim strFile As String
Dim i As Long
Dim oFrm As New UserForm1
    With oFrm
        .Caption = "Select files to attach"
        .Height = 272
        .Width = 240
        .CommandButton1.Caption = "Continue"
        .CommandButton1.Top = 210
        .CommandButton1.Width = 72
        .CommandButton1.Left = 132
        .CommandButton2.Caption = "Cancel"
        .CommandButton2.Top = 210
        .CommandButton2.Width = 72
        .CommandButton2.Left = 18
        .ListBox1.Top = 12
        .ListBox1.Left = 18
        .ListBox1.Height = 192
        .ListBox1.Width = 189
        .ListBox1.MultiSelect = fmMultiSelectMulti
        strPath = BrowseForFolder & Chr(92) 
        'If the files are always in the same folder you coiuld set strPath to that folder e.g.
        'strPath = "C:\Path\"
        strFile = Dir$(strPath & "*.pdf")
        While Not strFile = ""
            On Error GoTo err_Handler
            .ListBox1.AddItem strFile
            strFile = Dir$()
        Wend
        .Show
        If .Tag = 1 Then
            Set olItem = Application.CreateItem(olMailItem)
            Set olAttachments = olItem.Attachments
            For i = 0 To .ListBox1.ListCount - 1
                If .ListBox1.Selected(i) Then
                    olAttachments.Add strPath & .ListBox1.List(i), _
                                      olByValue, 1
                End If
            Next i

            olItem.Display
        End If
    End With
    Unload oFrm

lbl_Exit:
    Set olItem = Nothing
    Set olAttachments = Nothing
    Set oFrm = Nothing
    Exit Sub
err_Handler:
    MsgBox Err.Number & vbCr & Err.Description
    Err.Clear
    GoTo lbl_Exit
End Sub

Function BrowseForFolder(Optional OpenAt As Variant) As Variant
Dim ShellApp As Object
    Set ShellApp = CreateObject("Shell.Application"). _
                   BrowseForFolder(0, "Please choose a folder", 0, OpenAt)

    On Error Resume Next
    BrowseForFolder = ShellApp.self.Path
    On Error GoTo 0

    Set ShellApp = Nothing
    Select Case Mid(BrowseForFolder, 2, 1)
        Case Is = ":"
            If Left(BrowseForFolder, 1) = ":" Then GoTo Invalid
        Case Is = "\"
            If Not Left(BrowseForFolder, 1) = "\" Then GoTo Invalid
        Case Else
            GoTo Invalid
    End Select
lbl_Exit:
    Set ShellApp = Nothing
    Exit Function
Invalid:
    BrowseForFolder = False
    GoTo lbl_Exit
End Function