Once a proposal has been signed, it becomes a legally locked document so it can't technically be completely deleted. Your client always has the right to view a proposal they have signed.
However, we understand that sometimes you'll want to send a proposal as a test and sign it to see the whole process through to the end, or perhaps you have created a new agreement which supersedes a previous one, and you don't want this proposal interfering with your stats.
All you need to do in this case is click on the proposal from your Dashboard and you'll find "Hide" under the options tab. Hiding a signed proposal means that it will no longer affect your pipeline stats or reports. You'll still be able to access it via your account and anyone who was sent a link to it will still be able to view it.