Complete the form as best as you can and then just ask your employer to sign it- since they provided all the other docs already.
The Job Offer Form is a duplicate of many of the information already provided elsewhere. For e.g. Use the contents of the recommendation letter to put in the section of the form that asks why you were chosen. The company registration information can be used to answer some sections as well. Also, when it asks about the advertisement of the position, just remember what date you applied and when you were called and when you started- that gives an idea of the number of days it took to fill the vacancy- work smarter! Hope this helps.
I became PR on August 1, 2019 It was a long journey but it worked out for me!