What preposition is most suitable referring to the verb add and the object Google Docs?
I've just added an essay in, into or on Google Docs?
I feel that it is either on or to (or even onto) depending on what is the perspective of the speaker.
I've added/put/published the video on YouTube
Is taking the perspective of a certain platform (YouTube/SharePoint/ Google Docs), on which the file is now available
I've added/moved/transferred the file (on)to the SharePoint
Instead is taking the perspective of the file itself and its journey from the original location to its destination in the cloud
'in' can probably be used too, but I feel that it's better coupled with a different verb, e.g.
I've put/stored the file in the SharePoint/ a USB pendrive
Conveying the idea of something that is stored for later usage.
to add something to something
as in a collection of documents or a database of documents