A process for thermoforming a plate-like element of composite polymer material, in which a central region and a peripheral region surrounding said central region are defined, comprising: - providing a mould including a male member shaped in a configuration that it is desired to impart to said plate-like element, and a female member counter-shaped with respect to said male member, wherein said male and female members may be displaced between an operating position of said mould in which they are pressed against one another, and a non-operating position in which they are spaced from one another, - disposing said plate-like element on said mould such that its central region is positioned between said male member and said female member when displaced into the non-operating position, - holding the peripheral region of said plate-like element by a plurality of pins having a free end associated with said mould and engaged in a corresponding plurality of holes obtained in said peripheral region, - displacing said male member and said female member towards the operating position until they abut on said plate-like element and start to deform said plate-like element into the configuration of said male member and said female member, while continuing to hold the peripheral region of said plate-like element, - completing the displacement of said male member and said female member towards the operating position and maintaining them in said operating position for a predetermined time, so as to thermoform the central region of said plate-like element into the desired configuration, - displacing said male member and said female member into the non-operating position and removing said thermoformed plate-like element from the said mould, characterized in that said pins are disposed on a mobile frame which may be removed from said mould in order to move said plate-like element to and from said mould, while said plate-like element is held by said pins. - providing a mould including a male member shaped in a configuration that it is desired to impart to said plate-like element, and a female member counter-shaped with respect to said male member, wherein said male and female members may be displaced between an operating position of said mould in which they are pressed against one another, and a non-operating position in which they are spaced from one another, - disposing said plate-like element on said mould such that its central region is positioned between said male member and said female member when displaced into the non-operating position, - holding the peripheral region of said plate-like element by a plurality of pins having a free end associated with said mould and engaged in a corresponding plurality of holes obtained in said peripheral region, - displacing said male member and said female member towards the operating position until they abut on said plate-like element and start to deform said plate-like element into the configuration of said male member and said female member, while continuing to hold the peripheral region of said plate-like element, - completing the displacement of said male member and said female member towards the operating position and maintaining them in said operating position for a predetermined time, so as to thermoform the central region of said plate-like element into the desired configuration, - displacing said male member and said female member into the non-operating position and removing said thermoformed plate-like element from the said mould,