Here's an example.
[VBA]Sub test()
Dim wb As Workbook
Dim docProps As DocumentProperties
Dim docProp As DocumentProperty
Set wb = ActiveWorkbook
Set docProps = wb.CustomDocumentProperties

With docProps
.Add Name:="CustomNumber", _
LinkToContent:=False, _
Type:=msoPropertyTypeNumber, _
Value:=1000
.Add Name:="CustomString", _
LinkToContent:=False, _
Type:=msoPropertyTypeString, _
Value:="This is a custom property."
.Add Name:="CustomDate", _
LinkToContent:=False, _
Type:=msoPropertyTypeDate, _
Value:=Date
End With
For Each docProp In docProps
Debug.Print docProp.Name, docProp.Value
Next

End Sub

[/VBA]
in the hidden sheet(can it be xlveryhiddeen)?
Yes