Adjust the crop precisely with the corner magnifier

Automatic edge detection handles the vast majority of photos, but the hard ones — white paper on a white table, cluttered desks, dramatic angles — sometimes need a human eye. ToPDF's crop editor is built so that fixing corners takes seconds, even with big thumbs on a small screen.

Opening the editor

You'll land in the crop editor two ways:

• Automatically, when the scanner isn't fully confident about the edges it found. The corners come pre-filled with its best guess — usually you just confirm.
• Manually, any time, by tapping Adjust crop under the preview. Re-cropping is non-destructive: the original photo is kept, so you can adjust as often as you like.

The magnifier loupe

The classic problem with corner dragging: your finger hides the exact pixel you're trying to hit. While you drag, ToPDF shows a round magnifier above your finger with a 3× zoom and a crosshair — you can see precisely where the corner sits relative to the paper's edge.

1. Touch a corner handle — the loupe appears.
2. Watch the loupe, not your finger, and settle the crosshair on the document's corner.
3. Release. Repeat for any other corner that needs it.
4. Everything outside your selection is dimmed — what stays bright is what gets kept. Tap Apply crop.

Corner placement that gives the best page

• Place corners exactly on the paper's corners, not inside the text margin — the perspective correction uses them to compute the page's true shape.
• A couple of millimetres of background is harmless; cutting into the page is not. When unsure, err slightly outward.
• If the page is curled and has no crisp corner, aim for where the corner would be if flat.

Frequently asked questions

Why does the editor open by itself sometimes?

When the detected outline looks skewed or uncertain, ToPDF prefers to ask rather than silently produce a bad crop. The pre-filled corners are its best guess — confirm or nudge them.

Can I crop to just part of a document?

Yes — the corners can outline any region, for example one paragraph or the label on a box. Perspective is corrected for whatever quadrilateral you select.

I applied a bad crop. Is the photo lost?

No. Tap Adjust crop again — the editor reopens on the original photo with your last corners, and you can fix them.