How to change Annual Subscription to monthly

Acrobat DC is not available on 1 month terms. Sorry.  Acrobat is a 12 month commitment.  Cancelling early incurs a 50% penalty fee.  To avoid penalty fees, wait until your 12th month to cancel. 

https://account.adobe.com/plans

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How do I Cancel my Subscription?
https://helpx.adobe.com/manage-account/using/cancel-subscription.html
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Subscription & Cancellation Terms:
https://www.adobe.com/legal/subscription-terms.html

Do you mean an annual plan with monthly payments, or an actual one month at a time plan?

SOME programs are available Monthly https://community.adobe.com/t5/Get-Started/Being-charged-for-a-full-year-when-i-m-on-month-to-month/td-p/10248222 - links and pictures

Let me move this to the Account, Payment, & Plan forum for you, which is the appropriate forum for your question.

The Using the Community forum is for help in using the Adobe Support Community forums, not for help with specific programs, installation issues, or account issues such as subscription questions or billing problems, or generalized questions about Creative Cloud services.

* Product questions should be posted in the associated product community.
* Installation questions should be posted in the Download & Install community.
* Account issues, including subscription questions or billing problems, should be posted in the Account, Payment, & Plan community.
* Questions about the Creative Cloud desktop app or general questions about apps in the Creative Cloud should be posted to the Creative Cloud Services community.

For information on how to change your subscription plan, see: https://helpx.adobe.com/manage-account/using/change-plan.html