Hi there,
I’ve been using Odoo for a while and I was thinking that if Erpnext supports the inheritance just like Odoo does and what I mean by that is Add a custom field to Sales Invoice doctype for example from your custom module without going to doctypes list and then search for Sales Invoice doctype and then add custom field mannually.
Yes this is possible, checkout Customizing DocTypes
Once you add your custom field, click “Actions” → “Export Fixtures” A dialog will appear. Just select your app. Whenever you install your app this custom field will be added automatically.