Some memberships come with an agreement: a breeders' club contract, a trade account's terms. Stokk can send it to each new member after you review them, have them sign it on a private link, and issue the card as soon as they do.
Open the membership card from Membership cards, choose Edit, make sure Approve each sign-up is on and saved, and upload the agreement as a PDF under Agreement before the card. It is one document for everyone, up to 15 MB, and it is never public. A protected PDF (restricted editing or a password) is turned away: save an unprotected copy first. Uploading a new version gives it to everyone you send it to from then on, including a Resend; a link already out keeps the version it was sent with.
While they haven't signed, the sign-up sits under Agreement sent, waiting for their signature, with when it was sent. After three days they get one reminder. If the link runs out, the sign-up moves back up with Agreement link expired and shows on the dashboard again: use Resend for a new link. You can still turn a sign-up down at any point, or open Details and choose Approve without the agreement.
If the card can't be made right after they sign (the ERP is down, say, or they match a customer who needs a look), the signature is kept and the sign-up comes back under Sign-ups waiting with Agreement signed. The email to you says why. Use Try again or Approve; they get the card by email when it is made.
The signed copy is under Agreement on the member's card in Stokk, and under Details on a sign-up that is still waiting.