How to Edit Text in a PDF (and What Is Not Possible)
Why PDFs are hard to edit
A PDF stores where each piece of text is placed on the page, not a flowing paragraph. There is no reflow, and fonts are often embedded as subsets, which means the letters you need may not even be in the file.
The cover and replace method
The Edit text tool finds each line of text on the page. When you click one, it covers the original with a patch that matches the background and draws your new text on top. This is the approach most free editors use. It works well for corrections of a word, a date or a number.
Know the limits
The replacement text is set in Helvetica, so it will not always match the original font exactly. Most editors only hide the old words under the patch, which means they can still be selected or extracted, a real risk if you are removing an account number. 76 PDF avoids this by default: pages you edit are rebuilt as pictures, so the old words are gone. The price is that those pages stop being searchable. Untick the option if you need to keep the text layer, and then do not rely on the edit to hide anything confidential.
Better options for big changes
For large rewrites, go back to the original document, such as the Word or design file, edit it there and export a new PDF.
After editing
Add your signature, then compress or protect the file as needed.