If you want to conduct maintenance tasks on your Tomos SM 125 F then it is usually a good plan to own a Workshop Manual to use as personal reference in the event you want to know the best ways to take off a certain part for example Door and fit it again the right way.
Tomos SM 125 F Workshop Manuals will give you specified diagnostic details for your vehicle so if something is wrong it can help you find out what the issue is and how you can fix it. You will be able to analyse if this can be achieved yourself or in the event the job is just too big you could make a reservation for your SM 125 F into a decent friendly mechanic.
Tomos SM 125 F manual