Thanks you very much! Worked like a charm! here is my total code for those who have nearly the same situation or for those who want some inspiration .

Dim rst As DAO.Recordset
Dim strInputStart As String, strInputEind As String, strInputLng As String, booNotWholeNumber As Boolean, strInputmail As String
Dim Subject As String


booNotWholeNumber = False


strInputStart = InputBox("Start Factuur Nummer")
strInputEind = InputBox("Eind Factuur Nummer")




Set rst = CurrentDb.OpenRecordset("SELECT DISTINCT [factuurid] FROM [tbl_vh_factuur] WHERE (tbl_vh_factuur.factuurid Between " & strInputStart & " And " & strInputEind & " ) ORDER BY [factuurid];", dbOpenSnapshot)


Do While Not rst.EOF
    strRptFilter = "[factuurid] = " & rst![factuurid]
    Subject = Subject & rst![factuurid] & ", "


    DoCmd.OutputTo acOutputReport, "rpt_vh_factuur_reeks_CL_PDFYUKI", acFormatPDF, "K:\01-Administratie\Database\Yuki_Upload\VH" & "\VH-" & rst![factuurid] & ".pdf"
    DoEvents
    rst.MoveNext
Loop


Subject = Left(Subject, Len(Subject) - 2)


rst.Close
Set rst = Nothing


strInputStart = vbNullString
strInputEind = vbNullString


'----------Mail declaraties----------------
    Dim mess_body As String, StrFile As String, StrPath As String
    Dim appOutLook As Outlook.Application
    Dim MailOutLook As Outlook.MailItem
  


    Set appOutLook = CreateObject("Outlook.Application")
    Set MailOutLook = appOutLook.CreateItem(olMailItem)


    '--> path here
    StrPath = "K:\01-Administratie\Database\Yuki_Upload\VH\"
    strInputmail = InputBox("Voer Bestemmings Mail adres")


With MailOutLook
        .BodyFormat = olFormatRichText
        .To = strInputmail
                
        '--> *.* for all files
        StrFile = Dir(StrPath & "*.*")


        Do While Len(StrFile) > 0
            .Attachments.Add StrPath & StrFile
            .Subject = Subject
            StrFile = Dir
            
        Loop




        '.DeleteAfterSubmit = True
        .Send
    End With
   
'----------Mail declaraties----------------


MsgBox "Reports have been sent", vbOKOnly