Just Fill it > Save it > Validate it ( if this form has validation Button ) and Upload it .
So it has to be Filled > Saved > Validated , that is it , it does not needs to be signed with Pen because you are going to Digitally sign your complete application Online ( as a last step after uploading all required documents as your online authorization that u are submitting this form online ) .You just upload the saved forms which have Validate Button you need not to Print > Sign with Pen and Scan those forms .
As per my understanding If there is any form which has Validate button and you try to upload scanned PDF file then ( MyCIC website ) will give you an error that it is not able to verify the file which you are uploading. I believe that the forms with Validate Button are Smart forms and this online ( MyCIC website ) recognizes them and accepts them and automatically extracts data from these forms into their database. You can see that once you upload a validated form to ( MyCIC website ) then it will start displaying your name in MyCIC where u are uploading your documents.
Once you are done with uploading all the documents then the ( MyCIC website ) will ask you to Enter your First / Last name and Click on the Box which says ( I Accept these Terms and Conditions ) then this process will sign this application digitally by clicking on Next Button.
You need not to do any thing with Digital ID Signature in Adobe..!!
I hope it helps you.