Once you start the application it will ask you a few questions to determine eligibility. After that you will be taken back to the application process and will be provided with a list of forms you would have to fill in.
IMM5710 is the basic form but depending on each case, applicant might have to fill other forms (if you have a spouse, if you have a lawyer to represent you, background check, etc.). IMM5710 is validated in Adobe PDF Reader and you will be forced to fill all the mandatory fields. Since Open Work permit is not bound to a certain employer, as long as you indicate that your application is for Open Work Permit, you won't have to fill employer information. I did not fill it as I'm currently unemployed but you can call CEC and ask.
Photo is required which you can upload right there.