Workers who become autonomous by doing the same job

pA reader has sent us a very interesting query that deserves to be answered openly regarding the simultaneity of the work for others and own doing the same functions inside and outside the company. The case that does not expose is a fairly common case among professionals and workers of medium-high qualification or in technical areas. I reproduce below:/p
pI work as an engineer in an engineering company, with an indefinite contract of 40 hours per week; but I'm thinking of doing some project on my own in my free hours, which are quite a lot, and on weekends. I am thinking of becoming autonomous to be able to legally make and invoice this type of work to have an extra income./p
pCheck if there is an exclusive contractual relationship . There is no comment in the consultation, but it can be deduced that the work contract between the company and the engineer does not include an exclusivity agreement, nor any clause that a priori could prevent the w