How to sign documents on the site using digital signature?

Question

Electronic digital signature

Good afternoon!
There is a site where the user can upload documents and, if necessary, can sign them with an electronic digital signature. What are the implementation options for this?
I read articles on this topic, from which it is clear that in addition to installing modules on the server, the user himself must have special programs installed. This option is not entirely satisfactory, it is better to leave it as a last resort. Are there other ways?
On the website of public services, it seems there is an opportunity to sign a document (when submitting 3-personal income tax, it seems) without installing third-party programs, can anyone know how this is implemented?
Does anyone have experience with similar tasks?