Does the signer need an account to sign?

No. The signer needs no account and nothing to install. They receive an email, click the secure link, review the document and sign right in their browser (desktop, tablet or mobile).

An account is only required on the sender's side — that's you. Depending on the signature level you pick, the signer may have to confirm their identity (for example a code sent by SMS for an advanced signature), but that doesn't create an account for them.