Is it possible to create a "digital seal" to tell if a document has been opened? So, in real life we have a handful of ways to leave a physical mark on a packet to know if it has been opened without authorization (eg. you can use 'opened' security tapes, or you can put a signature or stamp right through the envelop opening). One thing i see these tells share, is that they are some sort of signature that self destructs on any attempt to open the package.

My question is if you can build a digital equivalent to these seals. I'm aware encrypting the packet is a way to ensure its confidentiality, but it requires the eventual recipient to know a secret to decrypt it. One scenario where I don't see this working is sealed wills/testaments (which should only be opened and read once the testator has actually died), in this case when the custodian of the will first receives it, the eventual recipients are still unknown (the testator could die many years in the future, by then many of the intended recipients could be gone too).
My first thoughts are, probably it's impossible, as it's always easy to make a bitwise copy of the &quot;sealed&quot; document, open it, and then deliver the unmodified one with its intact signature, but i wanted to know if someone with more experience in cryptography could come with a solution.
Encrypt your document, and embed a web address (and login details) in the packaging from which a reader can get the decryption key. The website must be trusted. The website logs will tell you when software has requested the key to decrypt it.
If you also want to protect confidentiality, encrypt with two keys. One is the usual private key used to protect confidentiality, that the recipient has been given securely, the other is the tamper seal that has to be obtained from the website.