Just a polite question, why don't you use Adobe Acrobat Reader to attach digital signature? You won't have to print any page, scan and then upload. Use that feature please.
If you are hesitant doing this, let me tell you that this is totally allowed in any forms of DIBP. You are okay to do that and in my opinion more secure as well.
If you are going to use this feature just make sure you make a new copy of the form as a backup because after attaching your signature to the form the form will no longer be editable (because of security) and will lock your information in read only format.
If you are going to use this option make sure you have Adobe Acrobat Reader DC (it's free too) not just Adobe Reader because this option is not available in Adobe Reader.
Despite all the information I have provided above, if you still don't want to use digital signature then use the following method.
1. Fill in the required form (by typing)
2. Rename that form with Typed keyword or similar i.e. Form 80 - Typed.pdf and save it.
2. Print just the signature page
3. Sign it and scan it
4. Create another PDF file with only that scanned image of signed page and rename it i.e. Form 80 - Signed.pdf
You can use any naming convention like Form 80 Part A, Form 80 Part B etc. Upload both of these files under same appropriate heading for example Form 80 in immiaccount.