Signature field showing as Text field

2024 update: I had a form that I had already created and didn't want to have to recreate.  After you've clicked "Prepare a form" and are in form editing mode, you can click the ... menu at the top of the Prepare a Form sidebar. The first option, "Remove e-signing options" will set the form options as if you did not click the "collect signatures" option when you made the form. No need to redo the whole thing! 

UPDATE 2024 (as the selected solution is outdated and doesn't work): In Acrobat, you must convert to the old version of Acrobat first by going to File > Disable New Acrobat. This didn't automatically work on my document, however, and I had to unfortunately recreate the PDF/prepare the form again once in the old version of acrobat. Also, this is mentioned below, but also make sure to NOT check the "This document requires signatures" box when preparing the form.

Hopefully this helps someone!

In the current version of Acrobat (whatever is most recent for April 2024), I found that clicking Prepare a Form and then leaving the "This document requires signatures" box unchecked resulted in being able to use the standard signature form fields. 

Ugg, how frustrating.  I realize this is an old string but thought I would post the solution.  Wasted several hours on something so simple but found this online that worked for me.

In Adobe Acrobat Pro DC, open the PDF. Click the Tools tab and under Prepare Form, click Open. At the screen stating: “Select a file or scan a document to begin” Adobe should already display the file you have opened in Step 1. If you need to change the file, then click on “Change File” and browse to the correct file.
a. Do not check the box next to: “This document requires signatures” (it changes which signature field options are available).
b. Recommendation: Change the Form Field auto detection to OFF by clicking “Change” and unchecking the last box in General for: “Automatically detect form fields,” especially if the files you are adding the digital signature field to are not forms. If you choose to keep the “Form field auto detection is ON” you may get form fields detected in error. If this happens, click on the fields you do not need and delete them. Do not leave fields that you do not need in the file because this will affect accessibility and compliance with Section 508.
c. You may get a message: “No form fields detected.” This is fine, especially if the document is correspondence or the file is not a “form.” Click Start. On the

Click on Tools - Prepare Form and then click on "More" at the right side of the window and then on "Revert to Acrobat Form".

Is this a Adobe Sign form?