How to combine scanned pages into one PDF
Scanners and phones often save each page as its own image. This guide shows how to put those pages into one PDF in the right order, straighten them, make the text searchable and keep the file a sensible size.
Worked example: a three-page renewal letter
In this test we scanned a fictional three-page tenancy renewal letter from Northfield Lettings. Pages 1 and 2 were JPG files of 2,480 by 3,508 pixels, about 1.1 MB each, and page 3 was a 2.8 MB PNG. Each page was slightly crooked.
JPG and PNG to PDF combined them into a three-page A4 PDF of 15,307,824 bytes. Clean up scanned PDF detected straightening angles of 1.2, minus 0.8 and 0.6 degrees, which matched the tilt we had added, and its combined download at 150 dpi was 3,067,978 bytes. Recognise document text then read all three pages in about 8 seconds and the searchable PDF was 3,114,124 bytes.
The recognised text was accurate apart from spacing: it read "Page 1 of 3" as "Page1 of3" on two pages. Compress PDF found no saving on this file, for the reason explained below.
Choose how to bring the pages in
- You have image files (JPG or PNG): use JPG and PNG to PDF.
- You have several PDFs, or a PDF plus some images: use Merge PDF, which accepts PDF, JPG and PNG files together.
- You have paper and a phone or laptop camera: use Scan to PDF to photograph each page in the browser.
Combine image files into one PDF
- Open JPG and PNG to PDF and select all the page images at once. Up to 50 images and 100 MiB in total.
- Check the order in the list. Use the move earlier and move later buttons, or remove an image you do not need.
- Set Image paper size to A4, Letter or Image size (96 dpi), and Image page orientation to Match each image unless every page should be the same way round.
- Leave Output as One PDF with every image. The default margin is 24 points.
- Select Download image PDF. The file is called converted-images.pdf.
Add scans to an existing PDF
Open Merge PDF and select every file in one go, for example a PDF you already have and the new page images. All the pages appear in one list, where you can move, rotate or delete them. Then select Export and Download PDF.
In our test we merged the searchable three-page letter with a two-page capture from Scan to PDF. The result had five pages and the text on the first three was still searchable. For more on page order, see combining and splitting PDFs in the right order.
Scan paper with your camera
In Scan to PDF, select Start camera and allow camera access when your browser asks. Select Capture page for each page, then Add pages to document. You can capture up to 20 pages in one session. Each page takes the shape of the camera picture rather than A4, so use Correct perspective in the next step if you want a squared-up page.
Straighten and tidy the pages
Do this before OCR. Clean up scanned PDF turns pages into images, so any searchable text added earlier would be lost.
- Open Clean up scanned PDF and select the combined PDF.
- For each page, select Detect straightening angle, then Apply suggested angle. Use Detect upright direction for pages that are sideways or upside down, and Correct perspective for photos taken at an angle.
- Adjust greyscale, brightness or contrast only if it helps, and compare the original and adjusted previews. Strong settings can erase faint writing.
- Choose a PDF scan resolution of 96, 150 or 300 dpi. The default is 150.
- Select Download combined scan PDF. Pages you did not adjust keep their current settings.
Make the text searchable with OCR
- Open OCR PDF and select the cleaned-up PDF. It starts by recognising the current page; select Cancel in that review to do the whole document instead.
- If the text is not in English, choose the OCR language in the editor panel. Then select Recognise document text. The review lists each page and each word with a confidence score.
- Check names, dates and amounts. You can correct a word or exclude a page.
- Select Apply text layers, then Export and Download PDF.
- Open the download and search for a few words from different pages.
Keep the file size down
The scan tools in RedactNinja PDF store page images in a lossless format. That avoids adding compression artefacts, but the files can be large. Compress PDF can reduce them afterwards: in our test the Balanced preset took the 3-page letter, with its OCR text, from 3,114,124 to 257,521 bytes, and the text stayed searchable.
Resolution is what controls the size. Choosing 150 dpi in Clean up scanned PDF cut our letter from 15.3 MB to 3.1 MB, and the text was still recognised accurately. 96 dpi makes smaller files but small print can become hard to read, so check before you choose it. If the PDF is still too big to send, see how to make a PDF smaller for email and split it by maximum size.
Check the finished PDF
Count the pages, check the order, and read the first and last lines of each page against the paper copy. OCR can misread similar characters such as O and 0, so check reference numbers individually. Our guide on why you cannot select text in a PDF explains how OCR works and where it goes wrong.
Every step runs in your browser on your device, including the camera feed, and your pages are not uploaded.