How to Enhance a Whole Batch of Scanned PDFs

Scanning is rarely a one-document job. You digitise a folder of invoices. You photograph a whole contract file. You inherit a box of records that needs to become searchable. What you end up with is a stack of PDFs, all with the same problem — grey backgrounds, shadows, soft text — and cleaning them up one at a time is exactly the sort of task that eats an afternoon.

The good news is that documents scanned in one session usually share the same flaws, which means they usually want the same fix.

The steps

1. Open Blackpdf's Enhance PDF tool.

2. Drop your files in. You can add multiple PDFs rather than doing them one by one.

3. Dial in the settings on the preview. Use the Before / After compare slider to get the result you want — Whiten Background for shadows and grey paper, plus Exposure, Contrast, and Sharpness to taste. The defaults (Whiten 75, Exposure 55, Contrast 60, Sharpness 40) handle most document photos as-is.

4. Click Enhance PDF and download the processed files.

When one set of settings works for everything

This is the question that decides whether batching is a good idea, and the answer is usually about how the documents were captured.

Batch them together when they share a capture session: the same scanner, the same lighting, the same room, the same afternoon. Those documents will have near-identical flaws — the same shadow gradient, the same grey cast, the same softness — so a single set of settings genuinely suits all of them.

Process separately when the sources differ. A folder mixing freshly-photographed pages with twenty-year-old faxes and a couple of clean flatbed scans has no common denominator. Settings that rescue the fax will blow out the clean scan; settings that suit the clean scan leave the fax unreadable.

The practical test: if you'd describe them all the same way ("these are all a bit grey and shadowed"), batch them. If you'd describe them differently, split them into groups and do a pass per group.

Sanity-check the result

The one risk with batching is that a setting which flatters your preview page quietly ruins page 40 of document 7. Two habits that prevent it:

• Preview a representative page, not the easiest one. If some documents are worse than others, tune the settings against a bad page. Settings that rescue the worst page will comfortably handle the good ones.
• Spot-check the output. Open a couple of the processed files and look at a few pages before you throw the originals away. Ten seconds, and it catches the case where aggressive whitening erased a faint signature or a pencil annotation.

Keep the originals until you've checked. Enhancement is not reversible — the output is a new, grayscale, re-rendered file.

Building it into a pipeline

If a scanned batch always gets the same treatment — enhance, then OCR, then compress — that repetition is exactly what Workflows exist for. You define the sequence once and run it on each new batch instead of clicking through three tools every month.

The order for a scanned batch is worth committing to memory:

1. Rotate anything sideways.
2. Enhance — the clean-up.
3. OCR — recognition is far more accurate on an enhanced page. See cleaning up a scan before OCR.
4. Compress — last, never before OCR.

Common questions

Do the same settings get applied to every page of every file?

Yes — that's what makes batching fast, and it's why the documents need to be similar. The settings you dial in on the preview are applied throughout.

Some documents came out over-processed.

Then the batch wasn't homogeneous enough. Pull the outliers out and run them separately with gentler settings — particularly anything faded, where whitening does damage. See enhancing a faded document.

Can I enhance and OCR in one pass?

They're separate operations, but a workflow chains them so you only click once. That's the closest thing to a one-pass batch pipeline.

Will this shrink my files?

Usually, as a side effect — the output is grayscale and re-encoded, which often lands smaller than a full-colour phone photo. But it's not a compression tool; for real size reduction, follow up with Compress PDF.

How many can I do at once?

Very large batches take longer, since every page of every file is re-rendered. If a batch is enormous, splitting it into a few runs keeps each pass responsive.

Wrap-up

1. Add your scans to Enhance PDF together.
2. Tune the settings against a representative (ideally bad) page.
3. Enhance, then spot-check the output before deleting the originals.
4. Group by capture session — similar documents batch well; mixed sources don't.

If the same batch always gets the same treatment, turn it into a workflow and stop clicking through three tools every month.