How to make an electronic document management with an editor in your service?

Question

Document flow

I'm doing a small service, which provides for something like a workflow.
There was an idea that users could create documents directly in their admin panel.
For example, he presses the "create an order" button, and has something like Google-docs, or an online Word, with a form of an order template for its organization, and he only has to enter the main text. Then it will be stored in the outbox, the outgoing number will automatically fit in, signed with a qr code, and so on.
The question is about the integration of something like an online text editor.
What is there that could be used for this task? Even open source is desirable.

Answer 1

libreoffice has a "server" mode: https://wiki.documentfoundation.org/Using_LibreOff...

Answer 2

https://habrahabr.ru/post/129262/