Set custom document properties with Word interop

Question

I want to set some custom document properties of a word document I'm creating in my C# code. To do this, I followed this MSDN article and came up with this code:

using Word = Microsoft.Office.Interop.Word; // Version 12.0.0.0
word = new Word.Application();
word.Visible = false;
Word._Document doc = word.Documents.Add(ref missing, ref missing, ref missing, ref missing);
logger.Info("Setting document properties");
Core.DocumentProperties properties = (Core.DocumentProperties)doc.BuiltInDocumentProperties;
properties["Codice_documento"].Value = args[3];
properties["Versione_documento"].Value = args[4];

Unfortunately, I get this error whenever it reaches the code:

HRESULT: 0x80004002 (E_NOINTERFACE)

Why is that? I used the interfaces exactly as described my MSDN, why doesn't it work?

I'm using Interop for office 2010 and .net 3.5

Answer 1

You need to use CustomDocumentProperties, not BuiltInDocumentProperties. See MSDN reference on using Custom Document Properties in Word (and MSDN video here). You also need to check if the property exists and create it before trying to assign its value.

Core.DocumentProperties properties = (Core.DocumentProperties)this.Application.ActiveDocument.CustomDocumentProperties;
if (properties.Cast<DocumentProperty>().Where(c => c.Name == "DocumentID").Count() == 0)
  properties.Add("DocumentID", false, MsoDocProperties.msoPropertyTypeString, Guid.NewGuid().ToString());
var docID = properties["DocumentID"].Value.ToString();