Thank you all for replying to my questions. :)

I have looked up the phrase in a dictionary.


fill in : phrasal verb
[transitive] to add information such as your name or address in the empty spaces on an official document: FILL OUT:
Please fill in your name and address in the space provided.
I spent over two hours filling in the application form.
Fill in the missing words.


fillout : phrasal verb
[transitive] to add information such as your name or address in the empty spaces on an official document: FILL IN:
It took a long time to fill out the application form.

Macmillan Publishers Ltd. 2002


I think both fill out a form" and "fill in a form" are right.


I believe the question above has two answers.


Have a nice day! :D