No it won't harm the seed but it may not germinate and if it does you won't get the same plant you took it from. Most pelargoniums are hybrids and as such you may end up with something that resembles 1 of it's ancestors or like none of them at all. The seed may even be sterile. Seed for sale from companies is bred in isolation or a greenhouse may make new plants from cuttings.

A much better way to get new plants is to take cuttings from the mother plant. I can tell you how to do it if you decide to go that route

Thanks for the advice. By the way, growing my own plants from seeds aims to select the plants most suitable for my climate. I had a bad experience with many nice-looking varieties which ended-up looking as if blown by a hair-dryer before August. I constantly find tougher ones for my future seed-grown plants.