You're not very precise in your statement. Editing a date can mean to edited a date field or a plain text showing a date in a PDF. The latter would require Adobe Acrobat while the other is doable with the free reader. So, for Reader you don't need a subscript at all for Acrobat you can use a subscription but you can also get a perpetual license you can use offline and for ever. It's up to you:
You mean, like Microsoft, who want you to pay for Word before you can edit a document? What do you think Adobe are there for? They exist to sell stuff, and there are freebies to get you hooked. The usual deal.