Work certifications are documents justifying the execution of the work units included in the work. These documents are used to make partial payments to the contractor. The work certification includes the sum of the works already carried out in a project, which are segmented into different items invoiced once these works have already been executed and which attend to a closed budget in order to guarantee in some way what has been carried out in the work process. It is also important to know that in order to carry out a correct certification of the work, all the modifications that are carried out during the project must be included.