Will this work on a PDF made from phone photos?

Yes — that is the primary use case. The auto-levels step removes uneven lighting and shadows, producing clean white backgrounds and dark text even from phone camera shots.

Does the output PDF stay editable/searchable?

No. Each page is rasterised to a JPEG and embedded as an image. The text is no longer selectable. This is the same result as a real scanner without OCR. The output is ideal for sharing, printing, or archiving — not for copy-pasting text.

How long does processing take?

Each page takes about 1–2 seconds on a modern device. A 25-page PDF completes in roughly 25–50 seconds. A progress bar shows the current page.

Will the output file be larger or smaller?

Photo-heavy PDFs usually become smaller — phone photos are large but JPEG at 144 DPI is efficient. PDFs with text layers may become larger since text is replaced with raster images.

Can I adjust the effect before processing all pages?

Yes. Upload the PDF, adjust presets and sliders, and see a live before/after preview of page 1 before clicking Apply. The settings you see on page 1 are applied identically to all pages.

What is the difference between the presets?

Document Clean is the default — moderate contrast, 2% background clipping, and sharpening. Soft Scan is gentler and preserves more mid-tones. Photocopy is the most aggressive: very high contrast with bold black text and pure white background.

How to Enhance a Scanned PDF Online Free (Clean Background, Sharpen Text)

PDFs created from phone photos or low-quality scanners often look washed out — grey backgrounds, soft text, uneven lighting. You need them to look like they came from a proper flatbed scanner. This guide shows you how to clean up every page automatically, for free, without any software.

The Problem with Phone-Photo PDFs

When you photograph a document with your phone and convert it to a PDF, you get:

Uneven background — shadows in corners, yellow/warm cast from room light
Soft or blurry text from camera focus or motion
Grey paper instead of white — hard to read and visually cluttered
Low contrast — dark text and dark background blend together

A proper scan fixes all of these. The PDF Scan Enhancer replicates what scanner software does: grayscale conversion, automatic level adjustment, contrast boost, and edge sharpening — applied to every page in one click.

How to Enhance a Scanned PDF (Step by Step)

Open the PDF Scan Enhancer.
Drop your PDF in or click to browse.
A preview of page 1 loads — click Enhanced (Page 1 preview) tab to see the effect.
Choose a preset: Document Clean (recommended), Soft Scan, or Photocopy.
Adjust sliders if needed (Brightness, Contrast, Background Clip, Sharpen).
Click Apply to All Pages & Download PDF.
A progress bar shows each page being processed. The enhanced PDF downloads automatically when done.

Free Tool

PDF Scan Enhancer — Clean Every Page Automatically →

Upload a PDF, preview the effect on page 1, then apply to all pages. White background, dark text, sharp edges. No upload to servers.

Understanding the Three Presets

Document Clean (default)

Applies 2% histogram clipping, moderate contrast, and edge sharpening. Best for typed text, printed documents, answer sheets, and books photographed under normal indoor light. The most common choice for PDFs made from phone photos.

Soft Scan

Lower contrast and no sharpening. Preserves fine pencil marks, handwriting, and mid-tones. Use this for handwritten notes, pencil sketches, or lightly printed text where the aggressive Document Clean preset makes fine strokes disappear.

Photocopy

Maximum contrast — bold black text, pure white background. Some fine detail is lost. Best for documents that will be printed or faxed, or PDFs where the text contrast needs to be as high as possible for OCR software.

How the Enhancement Works

Each page goes through four steps:

Render at 144 DPI — PDF.js renders each page at 2× the base PDF resolution (72 pt/inch × 2 = 144 DPI), producing a crisp raster image of each page.
Grayscale conversion — colour information is discarded using the standard luminance formula, removing colour cast from warm light or tinted paper.
Auto-levels — the tool analyses the pixel histogram and clips the darkest and brightest N% of pixels before stretching the remaining range to fill 0–255. This is what removes shadows and makes the background white even under uneven lighting.
Contrast boost and optional sharpening — a contrast factor formula increases tonal separation between text and paper, and an unsharp mask (2-pass box blur) makes text edges crisp.

The enhanced pages are embedded as JPEG images into a new PDF using pdf-lib. The output file dimensions match the original PDF exactly.

Tips for Best Results

Shoot in good light: Even with auto-levels, extreme shadows from a single lamp are harder to remove. Photograph near a window or under ceiling lights.
Increase Background Clip to 3–5% for PDFs taken under warm artificial light — this more aggressively whitens the background at the cost of slightly clipping very light text.
Use Soft Scan for handwriting — high contrast can cause thin pencil strokes to disappear.
Check page 1 carefully before clicking Apply — if shadows are still visible, increase the clip slider until the background looks clean in the preview.

After Enhancing: Next Steps

Compress: The enhanced PDF contains JPEG images — use the PDF Compressor to reduce file size further.
Add page numbers: Use the PDF Page Numbers tool to stamp page numbers on the clean output.
Merge multiple enhanced PDFs: The PDF Merger combines several enhanced files into one document.