Can I delete a public document?

Short answer. No, you can’t.

Long answer: Blockchains are append-only databases. Once a transaction has become part of the blockchain it is practically impossible to delete that data. sproof only stores hash references in the blockchain and without the original data it is impossible to learn anything about the document. However, you may choose to store documents publicly. In this case, it is not possible to delete these documents. You may revoke documents, but that only adds a flag in that documents history without changing the original entry.