Upholding rights in due time
Anyone can, within a defined time period after publication of the patent grant, oppose said patent. Otherwise, the patent is legally valid after the opposition period has ended. The patent is then valid retroactively from the filing date for the maximum validity period.
The opposition allows to cite reasons opposing the legal granting of the patent. After the opposition has been reviewed, the patent can be maintained, limited or revoked.
For this purpose, you need the means and possibilities to take action against the novelty or the inventive step.