Are there other ways to save data in the cloud (sharing files such as pdf and others) other than using firebase?

Solution 1: Ferdinand

Flutter is developed by Google and so is Firebase (as you probably know). Therefore most people use Firebase or Firestore if they want Cloud-based data persistence in their app as it is therefore the easiest and most effective way to (probably).

I have also used AWS Amplify, which can also be used as the cloud backend (see this video). And you can use Azure if you really want to. As mentioned in the replies, you need to be more technical with your question and define what you want to do.

Solution 2: Sobin Benny

Yes, ObjectBox (NoSQL) is an another option for you.

here's the link :

There are few more cloud options to opt, but FireStore and ObjectBox will give you more stability and flexibility in Flutter.