Dynamic filename in access exportwithformatting

I have a form which shows details of one business organisation at a time. The primary field is business registration number.

I also have few reports on same form which are always run for the business entity of that form. (meaning the query refers to [forms]![Org]![reg_no]

I have written a macro and converted to VBA. I want now access to save file with above reg_no. Eg for reg no U123AS it should save as

Share certificates U123AS.pdf

Below is the VBA code ;

==================
Function Macro1()
On Error GoTo Macro1_Err

   
    DoCmd.OutputTo acOutputReport, "Share Certificates", "PDFFormat(*.pdf)", "Share Certificates" & Format(Now(), "ddmmyyhhnn") & ".pdf", False, "", , acExportQualityPrint


Macro1_Exit:
    Exit Function

Macro1_Err:
    MsgBox Error$
    Resume Macro1_Exit

End Function