To make Pendent Seals (one method of many, I'm sure- this one is based on images of 1400-era French sealed documents and a description of a technique from the British Public Record Office):
Start with your nice parchment document, having left a few inches unwritten at the bottom. Fold the bottom edge up. I wet a stripe with a small brush to create a foldline, then burnish the fold with a smooth bone or stone tool and clamp the folded part under a ruler taped to my desk until it's dry.
In my reference documents, the signature text is written on this folded-up portion. The cord for the seal is threaded through both layers- punch holes with a sharp awl, using a backing to avoid creasing the parchment.
Thread the cord, making a "stitch" across the front.
Bring the ends of the cord through this loosened "stitch".
Pull the loop down to make a V with the ends hanging neatly from the bottom edge of the document.
Knot or tie the cords together to make a Y shape. In all the reference documents, the ends of the cord emerge from two separate points on the seal.
Soften a lump of wax in hot (not boiling) water to a malleable point. Flexible wax with a high beeswax content rather than a brittle shellac-heavy wax will work best for this. Roll the wax into a ball.
Press the ball onto the seal matrix, pressing it well to make a good impression. Note where the top of the image will be.
Lay the cords across the wax, aligning so that the image will be right-side-up.
Flip the document and seal over and press well against a non-stick backing, in this case a piece of foil.
Soften a second lump of wax, about the same size as the first, and roll it into a ball. Press this onto the back of the first, sandwiching the cords. Shape the edge into an attractive finish. Note that the seal matrix (in this case, a signet ring) is still in the face of the wax.
Remove the wax from the matrix and admire your handiwork.