Flatten PDF

Form fields, comments, highlights, stamps and drawings are annotations: objects that float above the page and that a reader can move, edit or hide. Flattening draws each into the page content itself, from the very appearance the viewer shows and at the exact place, then removes the annotation. The page looks the same, but it is now ink - the same in every viewer and on paper.

No. The values are drawn in and the form definition is removed, which is the point: a signed or completed form that nobody can change afterwards. Keep the fields if you want to keep it fillable, and flatten only the markup.

Some producers save a form without appearance streams and leave it to the viewer to draw the fields. There is nothing to burn in then, and the tool counts those fields. Filling the form with the Fill forms tool first gives every field an appearance.

Nothing is uploaded: the file is opened and processed inside your browser and never leaves your device. Close the tab and it is gone.

No - links are left alone by default, because a link is navigation, not decoration: flattening it would draw its box and take the click away. There is a switch to remove them when you want a document nothing can be clicked in.

Flattening rewrites the file, which breaks the signature - the document keeps its look but no longer verifies. The tool marks a signed file with a warning instead of refusing it, because making a flat copy for printing or forwarding is a fair thing to want.