To further bump, AttachmentManager.getAttachment is deprecated. AttachmentService is annotated as @ExperimentalApi.
I can’t find any way to read the attachment contents using AttachmentManger. Looking at the source code AttachmentService uses AttachmentManagerInternal to create and update attachments.
AttachmentService also doesn’t support minorEdit for noiseless deletion, API Notifications for Removing Attachments
So, which is the recommended API, manager or service, deprecated or experimental?