How the mirror line is chosen on each page

The center of what you can see

A mirror needs a line to reflect across. Flip pages uses the middle of the visible area of each page, not the middle of the full sheet stored in the file.

That matters for pages that were cropped. Say a scan was cropped to remove a wide black border on the left. If the flip used the full sheet, the visible part would land off-center, and some of the trimmed border could slide back into view. Using the visible area means the cropped page mirrors onto itself, and the crop stays where it was.

Pages of different sizes in one file are handled one by one, each with its own center. A landscape fold-out in the middle of a portrait report flips around its own middle, not the report's.

Rotated pages

Some PDFs store a page sideways and add a setting that tells readers to turn it 90 degrees when showing it. Scans and slides exported to PDF often look like this.

"Horizontal" always means left to right as you see the page on screen, and "Vertical" means top to bottom as you see it. On a page with a 90 or 270 degree rotation setting, the tool swaps the axis internally so the result matches what you picked. The rotation setting itself isn't touched, so the page still opens the same way round.

How comments keep their place

Comments are separate objects with their own coordinates, so the tool moves each one to the mirrored spot. It doesn't just move the outer box. It recalculates the points inside:

• Highlight, underline and strike-out comments store the corners of every marked piece of text. Those corners are mirrored, so a highlight still sits over the same words after the flip.
• Freehand drawings are mirrored stroke by stroke.
• Lines, arrows and polygon shapes have each end point or corner moved.

What isn't changed is how a comment draws itself. A sticky note icon or a text box comment moves to the right place but still reads normally.

Working out which flip a scan needs

When a scan or export comes out wrong, look at a letter such as R or the number 7:

1. Letters reversed, top of the page at the top: choose "Horizontal".
2. Letters reversed, page upside down: choose "Vertical".
3. Page upside down but the letters aren't reversed: it isn't mirrored. Use Rotate PDF instead.

If only some pages are wrong, for example the backs of double-sided originals, type them into "Pages", such as "even".