Open the field’s authoring properties
In Acrobat’s form-authoring workflow, use All tools > Prepare a form, then select the relevant text field and open its Properties. Work on a copy when changing a reusable form.
Merely clicking inside a field as a recipient is not the same as opening its authoring properties; the form’s permissions and your available tools determine what you can change.
Use Appearance for text settings
The Appearance tab provides Font Size, including Auto for dynamic fitting, as well as Font and Text Color where applicable. Pick the setting that serves the expected entry rather than only a short sample.
Changing a field’s border dimensions is a separate Position or resize operation. A larger rectangle does not by itself specify a new font size.
Check a realistic long entry
Try a long name and a multi-word answer. With Auto, text may shrink to fit; a fixed size may reveal that the field needs more room.
As the author, consider the longest reasonable response and the printed result. As a recipient without editing permission, ask the issuer for an adjusted form rather than assuming every PDF viewer exposes the same authoring controls.
Separate other PDF text tasks
For ordinary page text, read Acrobat font editing. To inspect the document’s font list, use identify fonts in a PDF. These workflows answer different questions.
Your questions, answered.
Why can I type but not change the field font?
Filling a form does not necessarily grant access to its authoring properties. Permissions and the available application tools matter.
Does Auto always keep the same size?
No. Auto can resize the text to fit the field.
Sources & background
Sources supporting this page’s explanations. Practical examples are our editorial suggestions.