Can I change the original printed text inside the PDF?

This editor is best for page cleanup and overlay-style editing such as annotations, text boxes, shapes, images, tables, and white cover boxes. It does not currently rewrite the original PDF text objects directly.

Is whitener the same as secure redaction?

No. Whitener visually covers content in the exported PDF, but it should not be treated as permanent redaction for sensitive information.

Should I edit before or after compressing?

Edit first, then compress. That avoids optimizing pages you are going to remove anyway and lets you review the final layout before reducing file size.

How to Edit a PDF in Your Browser with Annotations, Shapes, Tables, and Whiteout