Contrast PDF.

Manual contrast is useful when the page is generally even but the lettering looks weak. Increase contrast gradually; use brightness to keep the paper from becoming too gray or the letters from fading.

The starting settings are not a verdict about your document. Compare a thin punctuation mark or pale handwritten note before applying a stronger adjustment.

Auto levels changes the relationship between the light and dark values in the page. Strength controls the amount; clipping affects how much of the extremes is discarded.

A clean background is not the only goal. If a pale signature or a highlight disappears, reduce the effect or return to Manual contrast.

Local contrast has its own amount and detail controls. It can make nearby light and dark features easier to distinguish in a scan with uneven tones.

It can also emphasize paper texture, noise and halos. Inspect the small print and any photograph rather than judging the result only from a zoomed-out page.

Keep shared settings only when the source pages need the same treatment. A dark photocopy and a pale original may need different adjustments.

The final PDF contains rendered page images at the chosen 150, 200 or 300 DPI. Run PDF OCR afterward when you need recognized text; existing searchable text is not retained by this conversion.