You can apply for PIP whilst in full time work. Your claim will need to show how your disability affects you on a day to day basis and what help you need although you do not need to actually be receiving that help. Bear in mind that you will need to show that your employment isn't at odds with the information you put on your claim form. As an example if you put that you have mobility issues but your job involves a lot of walking then the assessor may consider that mobility issues are limited.
Nothing on this board constitutes legal advice - always consult a professional about specific problems
