I have 7.0, but assuming your VBA code does something like (where cPDF is your document)
AcroApp = CreateObject("AcroExch.App")
AvDoc = CreateObject("AcroExch.AVDoc")
PDDoc = CreateObject("AcroExch.PDDoc")
If AvDoc.Open cPDF,"" Then 'pdf document is open
then to fill in form data, something like
AcroForm = CreateObject("AFormAut.App")
Fields = AcroForm.Fields
For Each f in Fields
If f.type="Text" Then Fields.Item(f).Value = "something"
Next f
If your form has radio buttons, other types of controls or you need fields marked as readonly after data is entered, it gets more complicated, so you might want to post a copy of the pdf. .02 Stan