I recently encountered this problem too. The site https://hd-stamp.com was very helpful. There you can create your own seal for free - round, square or even triangular. A very simple and clear designer. Choose a shape, enter text, you can add graphics. Just three clicks - and the layout is ready. I saved it in PDF format and immediately inserted it into the contract. There is a PDF editing function right on the site. In addition, you can restore a lost seal by imprint - this is generally cool! The service has been operating for 12 years, they have a great reputation.