Open any PDF file, and if Preview recognizes that it contains form elements, an "AutoFill Form" button appears in the upper-right corner of the PDF window. Click it, and the page is now populated with editable fields highlighted in pale blue. You can now click in a field to add text or click the field and drag its location. If you decline to click or it seems like Preview hasn’t recognized there were fields on a page, you can click the new "Show Form Filling Toolbar" icon, which looks like a long rectangular with an ellipsis in it (…) and a thin pencil angled at far right.

The process isn't perfect. Preview sometimes only generates some of the necessary text boxes. You can add more by holding Option and dragging a field to a new position. That new field lacks the blue highlighting.

If you want to add additional text or other elements, you can use the Form Filling Toolbar items, which include buttons for redacting text, adding a scanned or mouse/stylus written signature, and adding text fields. For even more control, click the "Show Markup Toolbar" button in the main toolbar, which looks like a marking pen inside a circle.

It turns out you can still access all the traditional image format options from the Save and Export panels just by holding down the Option (Alt) key when clicking on the Format menu.

Holding the Option (Alt) key when selecting format reveals all possible image formats. You can use this to convert existing images to different formats, or to save the file as a less common format.