Hi, I signed up for a "free trial" today only to find that I couldn't sign the document I needed on

Don't worry.  You have 14 days from the date you joined to cancel without penalty.

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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

CONTACT ADOBE SUPPORT:
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Online Chat: https://helpx.adobe.com/contact.html?rghtup=autoOpen
Phone M-F, during normal business hours: https://helpx.adobe.com/contact/phone.html

Please go to Adobe Customer Service (make sure to sign into your Adobe account first) :
https://helpx.adobe.com/contact.html?rghtup=autoOpen will automatically open the chat window.
Type "Agent" in the chat box to bypass the chatbot and be connected to a person.

You may also be able to contact Adobe by phone:
https://helpx.adobe.com/contact/phone.html

Moving this to the Account, Payment, & Plan forum as it appears to be a subscription issue.

The Using the Community forum is for help in using the Adobe Support Community forums, not for help with specific programs or with billing/account issues. Product questions should be posted in the associated product community. Billing and account issues should be posted in Account, Payment, & Plan.