I had the same dilemma like you. I posted here nobody answered
However, from my understanding the letter they sent is very generic and the signature part is for additional forms, if they request. One of the documents they requested from me is my marriage certificate, which by any means I cannot scribble on. I just submitted scanned all my docs trough my portal. I haven’t got anything back from ircc since I uploaded the docs, which was beginning of the month. It says under review on all of them. Hope this makes you feel better. Not sure if it helps.