If you wish to perform auto repairs on your own Yamaha WR 400 F then it will always be a good plan to possess a Workshop Manual to use as personal reference if perhaps you need to know tips to remove a specific part including Door and fit it again successfully.
Yamaha WR 400 F Workshop Manuals will give you detailed diagnostic info for the car or truck therefore if something is faulty it can help you work out what the problem is and easy methods to make it better. Then you are able to analyse if you can do this by yourself or that the job is just too big you could book your WR 400 F into a suitable mechanic.
Yamaha WR 400 F manual