Formatted fields

I have a document template(attached - Basic Letter.doc) from which I am creating a document. In the template, the DOS field has a switch to display the format as January 1, 2010 - {DOCPROPERTY "~DOS" \@ "MMMM d, YYYY" }.
Using Aspose, I pass the values into the custom document properties & then update the fields:

doc.CustomDocumentProperties["~PtFirst"].Value = firstname; 
doc.CustomDocumentProperties["~PtMiddle"].Value = middlename; 
doc.CustomDocumentProperties["~PtLast"].Value = lastname; 
doc.CustomDocumentProperties["~DOS"].Value = dateofService; 
doc.Range.UpdateFields();

However, in the final saved document(saved.doc), the formatting is not put in. The date instead displays as 01/01/2010.
What can be done about this?

Hello

Thanks for your request. I cannot reproduce the problem on my side using the latest version of Aspose.Words (8.1.0). You can download this version from here:
https://releases.aspose.com/words/net
I use the following code for testing:

Document doc = new Document("in.doc");
doc.CustomDocumentProperties["~DOS"].Value = DateTime.Now;
doc.UpdateFields();
doc.Save("out.doc");

Best regards,