Text Boxes - how to protect from moving or editing

Unless you want to protect your form with a password, there is nothing you can do to prevent anybody from moving your fields around.

Keep in mind that "password protection" does not mean that you need to use a password to open the document. There are two ways you can assign a password to a document: It can be used as an "open" password, which means that you need to enter that password every time you want to open the document, but there is also an "owner" password, or a "permissions" password that allows you to protect the document so that it cannot be edited anymore, but still allows a user to just open it and e.g. fill out a form. Both of these passwords are assigned via the "Document Properties>Security" dialog (Ctrl-D or Cmd-D, then select the "Security" tab).

Karl Heinz Kremer
PDF Acrobatics Without a Net
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As it has been said, you can set an owner password.

Another, also soft, procedure would be to set the position of the field at certain given events (such as document open, or Page Open) to a predefined value. Your user can move the field, but the next time that event is triggered, the field gets back to its original place.

Hope this can help.

Max Wyss.

Using Acrobat Pro XI you can create a self-signed digital ID and Certify your PDF form allowing users to change only form fields and sign the document. Certifying signatures can be visible or invisible.

Take a look at:
https://helpx.adobe.com/acrobat/using/certificate-based-signatures.html#certifyingandsigningdocuments
https://helpx.adobe.com/acrobat/using/digital-ids.html#digital_ids