How to Set a custom property in a word processing document

class Program
    {
        static void Main(string[] args)
        {
            const string fileName = "SetCustomProperty.docx";
            Console.WriteLine("Manager = " +
                SetCustomProperty(fileName, "Manager", "Peter", PropertyTypes.Text));
            Console.WriteLine("ReviewDate = " +
                SetCustomProperty(fileName, "ReviewDate",
                DateTime.Parse("12/21/2010"), PropertyTypes.DateTime));
        }
        public enum PropertyTypes : int
        {
            YesNo,
            Text,
            DateTime,
            NumberInteger,
            NumberDouble
        }

        public static string SetCustomProperty(
            string fileName,
            string propertyName,
            object propertyValue,
            PropertyTypes propertyType)
        {
            // Given a document name, a property name/value, and the property type, 
            // add a custom property to a document. The method returns the original
            // value, if it existed.

            string returnValue = null;

            var newProp = new CustomDocumentProperty();
            bool propSet = false;

            // Calculate the correct type.
            switch (propertyType)
            {
                case PropertyTypes.DateTime:

                    // Be sure you were passed a real date, 
                    // and if so, format in the correct way. 
                    // The date/time value passed in should 
                    // represent a UTC date/time.
                    if ((propertyValue) is DateTime)
                    {
                        newProp.VTFileTime =
                            new VTFileTime(string.Format("{0:s}Z",
                                Convert.ToDateTime(propertyValue)));
                        propSet = true;
                    }

                    break;

                case PropertyTypes.NumberInteger:
                    if ((propertyValue) is int)
                    {
                        newProp.VTInt32 = new VTInt32(propertyValue.ToString());
                        propSet = true;
                    }

                    break;

                case PropertyTypes.NumberDouble:
                    if (propertyValue is double)
                    {
                        newProp.VTFloat = new VTFloat(propertyValue.ToString());
                        propSet = true;
                    }

                    break;

                case PropertyTypes.Text:
                    newProp.VTLPWSTR = new VTLPWSTR(propertyValue.ToString());
                    propSet = true;

                    break;

                case PropertyTypes.YesNo:
                    if (propertyValue is bool)
                    {
                        // Must be lowercase.
                        newProp.VTBool = new VTBool(
                          Convert.ToBoolean(propertyValue).ToString().ToLower());
                        propSet = true;
                    }
                    break;
            }

            if (!propSet)
            {
                // If the code was not able to convert the 
                // property to a valid value, throw an exception.
                throw new InvalidDataException("propertyValue");
            }

            // Now that you have handled the parameters, start
            // working on the document.
            newProp.FormatId = "{D5CDD505-2E9C-101B-9397-08002B2CF9AE}";
            newProp.Name = propertyName;

            using (var document = WordprocessingDocument.Open(fileName, true))
            {
                var customProps = document.CustomFilePropertiesPart;
                if (customProps == null)
                {
                    // No custom properties? Add the part, and the
                    // collection of properties now.
                    customProps = document.AddCustomFilePropertiesPart();
                    customProps.Properties =
                        new DocumentFormat.OpenXml.CustomProperties.Properties();
                }

                var props = customProps.Properties;
                if (props != null)
                {
                    // This will trigger an exception if the property's Name 
                    // property is null, but if that happens, the property is damaged, 
                    // and probably should raise an exception.
                    var prop =
                        props.Where(
                        p => ((CustomDocumentProperty)p).Name.Value
                            == propertyName).FirstOrDefault();

                    // Does the property exist? If so, get the return value, 
                    // and then delete the property.
                    if (prop != null)
                    {
                        returnValue = prop.InnerText;
                        prop.Remove();
                    }

                    // Append the new property, and 
                    // fix up all the property ID values. 
                    // The PropertyId value must start at 2.
                    props.AppendChild(newProp);
                    int pid = 2;
                    foreach (CustomDocumentProperty item in props)
                    {
                        item.PropertyId = pid++;
                    }
                    props.Save();
                }
            }
            return returnValue;
        }
    }