Do I need some kind of licence or any papers if I want to sell a pcb board that I made to different people?
tl;dr: it takes more than a QC Passed sticker, but some self-testing and checking the datasheets for harmful stuff can be enough for a start.



As a business selling electronic products in the EU, you must:


Put some labels on the product indicating the name of your company, the name of the product, what battery type it uses.
Have a manual explaining how the product should be used, and shouldn't be used (a link to download a PDF is ok).
Make sure you product is not dangerous to use. Are there sharp corners, pieces that can cut? Can a kid insert its finger in the products? If the product falls, does it brake in dangerous fragments?
Check for interferences (spurs), even if there is no radio on your product. For a quick self-test you can borrow/rent a spectrum analyzer. For a real test, you must pay for a certification laboratory.
Check if your product still works ok in the presence of interferences generated by other products. Hard to self-test, use a certification lab.
Make sure your product does not contains harmful substances (lead, toxic flame retardants, mercury, etc). Using a lead-free process is just a small part, you also have to check what goes into the parts you build your product with.
Register to an electronic waste collection program (country specific). In France you have to collect a small tax on each product sold and give that to an independent organization so they could pay for the safe recycling of your products even if you company doesn't exist anymore.
Be aware of all the tax stuff (country specific), VAT and all. Sometimes there are simplified rules for small companies of individuals.


If you are selling kits, or experimental products, in small quantities, there is some tolerance. You can do some basic tests yourself to check, with a reasonable certainty, that the product is suitable and not dangerous.

But you have to inform yourself, way beyond what you can learn on Stackexchange, as you're ultimately responsible for what you sell. Ignorance is not an excuse, as all documents are available in all EU languages. Waivers that put all the responsibility on the customer are invalid. Lastly, if your product is competing with a commercial product, there is no tolerance and you must pass full certification, otherwise this would be unfair competition.