In the Czech Republic, it seems like we are constantly completing forms – at the bank, at the post office, on the internet, everywhere. But be careful – we are not ‘fulfilling’ the forms, we are just ‘filling’ them.
Well, actually, you can say it three ways. You can ‘fill’ the form, you can ‘fill in’ the form (more British) or ‘fill out’ the form (more American).
To fulfil means something else. It means that either you are able to complete a task, or you meet the criteria for something. To get a job as a lifeguard, for example, you need to fulfil the requirements, i.e. being able to swim to a high level, no health problems etc. If you fulfil the requirements then they might consider you for the job.
Or when you are working in the office, you need to fulfil your duties, meaning you need to complete all the tasks asked of you. So, for example, a typical sentence might be: „The chef was fired because he failed to fulfil all his work duties.“