Hi Senad,

You can add custom document properties with something like the following:

ActiveDocument.CustomDocumentProperties.Add _
   Name:="YourName", LinkToContent:=False, Value:="Value", _
   Type:=msoPropertyTypeString

For more reading, you can check out "How to use a single VBA procedure to
read or write both custom and built-in Document Properties" at
http://word.mvps.org/faqs/macrosvba/MixedDocProps.htm

As for having multiple values per property: in theory, I think you can if
the value type is text and THEN you parse that text as an array, but I
haven't tested this.
Ummm just tested it, and it works (there might be maximum length limits for
these values):

Dim sValues
ActiveDocument.CustomDocumentProperties("YourName").delete

ActiveDocument.CustomDocumentProperties.Add _
   Name:="YourName", LinkToContent:=False,
Value:="Value1,Value2,Value3,Value4", _
   Type:=msoPropertyTypeString
sValues = Split(ActiveDocument.CustomDocumentProperties("YourName").Value,
",")
Debug.Print ActiveDocument.CustomDocumentProperties("YourName").Value
For iCount = 0 To UBound(sValues)
   Debug.Print sValues(iCount)
Next iCount

HTH,

Dave