Most services that store your documents can read them. Not maliciously — it is simply how the architecture works: the file arrives, the server decrypts it to process it, and from then on access is a policy question rather than a mathematical one.
The alternative moves the key
End-to-end encryption means the content is sealed on your device, with a key derived from something only you know, before it is transmitted. What the server stores is ciphertext. Not "ciphertext it could decrypt if asked" — ciphertext it has no key for.
This changes the threat model completely. A breach of the storage yields nothing readable. A subpoena to the service yields nothing readable. An employee with database access sees the same nothing.
And it comes with a real cost
There is no password reset. If the recovery phrase is lost, the data is gone — not withheld, gone, in the same way a shredded document is gone. Any system that offers real end-to-end encryption and a friendly "forgot password" link is offering one of the two, and it is not the first.
Encryption you can be talked out of is not encryption. It is a policy with good branding.