I currently pay for Adobe Acrobat Pro @ $19.99 a month. I also have a subscription for Adobe Standard @ $12.99 a month. Is this necessary to have both of these plans?

Unless you’re using Acrobat on more than two machines (that’s the limit of installing one Acrobat license), I would say no. Everything in Acrobat Pro is in the Standard version, and more.

I don’t speak for Adobe I’m an end user just like you. But I can say if you have Acrobat Pro, you don’t need the Standard subscription too. 

Hope this helps,

Randy