How can I save a PDF file in Parse and then save changes while the user is editing the document and if the file same file is open on other devices allow them to edit the document and it'll appear on devices with the files open. So like 'collaboration PDF editing'. But I want the changes made to the file to appear on other devices almost instantly with almost no delay. (iOS App, Swift)
Parse would be a bad choice to achieve this kind of functionality because it does not allow for real-time streaming or updates.
The closest thing you could get with Parse would be to use afterSave cloud hooks to send push notifications to the other devices which instructs them to refresh the file with the latest data.
What you are looking for is something like PubNub Data Streams or FireBase RealTime Database.