DocumentOverriedePreserverFields.cs

/// <summary>
/// An item is being updated.
/// </summary>
public override void ItemUpdated(SPItemEventProperties properties)
{
    base.ItemUpdated(properties);

    // Get Current ListItem
    SPListItem item = properties.ListItem;
    
    // Check if Title is Null Or Empty. 
    // Title will be empty in case user is uploading the new document without any property. Same time Title field should be mandatory field.
    if (string.IsNullOrEmpty(item.Title))
    {
        // Get Before Properties
        var beforeProperties = properties.BeforeProperties;
        
        // Loop and update all the properties
        foreach (System.Collections.DictionaryEntry prop in beforeProperties)
        {
            try
            {
                if (prop.Key.ToString().Equals("vti_title"))
                {
                    item["Title"] = beforeProperties[prop.Key.ToString()];
                }
                if (item.Fields.ContainsField(prop.Key.ToString()))
                {
                    var field = item.Fields.GetField(prop.Key.ToString());
                    
                    // Check if it is valid property
                    if (item.Fields.ContainsField(prop.Key.ToString()) && !field.ReadOnlyField && !field.Sealed)
                    {
                        item[prop.Key.ToString()] = beforeProperties[prop.Key.ToString()];
                    }
                }
            }
            catch
            { }
        }

        // Update the ListItem
        EventFiringEnabled = false;
        item.SystemUpdate();
        EventFiringEnabled = true;
    }
}