SPID - I think I'll need one of these in

SPID - I think I'll need one of these in order to register my business, and also for some other things.

I've requested one from Aruba.it. At the final step I need to download a PDF, digitally sign it, and upload it. There are two problems with this.

The first is that I can't open the PDF - not with Adobe, not with "Dike GoSign". Both say that the file is unreadable.

The second is that I need a digital signature/certificate. This takes me to:

https://www.pec.it/acquista-firma-digitale-remota.aspx

I think this is the thing that I need first, preferably not the smart phone option as I'd like to be able to use this on and from my PC.

Am I right in thinking that when I have that I can download the software mentioned called "ArubaSign" and I'll then be able to open that PDF and sign it digitally, so as to complete the request for the SPID?

There is the option to validate the SPID request in-person but the nearest office is some distance from here,and having a personal digital certificate would probably be useful for some other things later. Thanks.