How to Turn Pictures Into a PDF: Sizes and Quality

Turning photos or scans into a PDF makes them easy to send as one document, print in order, and keep together. This guide explains how pictures become pages, how to choose a page size and margin, what happens to quality, and how to keep the file a reasonable size.

One picture, one page

The tool puts each picture on its own page, in the order of your list. You can move pictures up and down before you make the file, which is easier than rearranging pages afterwards. Common uses are a set of scanned pages from your phone, photos of a receipt and a form, or a series of screenshots to share as one file.

Choosing the page size

• A4 is 210 by 297 millimetres, which is 595 by 842 points in PDF terms (a point is 1/72 inch). It is the standard paper size in India and most of the world.
• US Letter is 8.5 by 11 inches, or 612 by 792 points, used in the United States and Canada.
• Same size as each picture makes every page exactly as large as its picture, with no margin. That is best for screens, such as screenshots, because nothing is shrunk.

On A4 or Letter the tool picks portrait for a tall picture and landscape for a wide one, and scales the picture to fit inside the margin, centred on the page. It keeps the shape of the picture so that nothing is squashed, and a small picture is enlarged to fit, so it may look soft if it has few pixels. Margins of none, small and normal are offered, and a normal margin of about 13 millimetres is safe for most home printers, which cannot print right to the edge.

What happens to quality

JPEG is a lossy format, and every time a JPEG is compressed again, a little more detail is lost. To avoid this, the tool puts JPG and PNG files into the PDF as they are, without compressing them again, so the quality is the same as the original. The exceptions are pictures that need work first. WebP files cannot be placed directly, so they are redrawn as PNG, which is lossless. A JPG photo that is stored sideways with a rotation note (an Exif orientation tag) is redrawn upright and saved as JPEG at high quality, since otherwise it would appear on its side in the PDF.

Keeping the file size down

The size of the PDF is mostly the size of the pictures. A modern phone photo is often 3 to 8 MB, so ten photos can make a file of 50 MB or more, which many email systems reject. If the file is too large, shrink the pictures first with an image resizer or compressor before you make the PDF. For documents, a width of about 1600 to 2000 pixels is enough to read and print a page clearly. PNG files from screenshots can also be large, so convert photographs to JPG, which is better suited to photographs, before building the PDF.

Scans and readability

A PDF made from pictures is a set of images, not text. You cannot search or select the words unless you run text recognition (OCR) with another tool. For official use, make sure the scan is straight, well lit and readable at full size. If text looks small or blurry, retake the picture rather than enlarging it, because enlarging cannot add detail.

Privacy

Photos and scans often contain private details. The pictures are processed in your browser and not uploaded. Remember that photos can also carry hidden camera and location data in their files; the PDF made here places the picture itself on the page, but you may want to clean the originals with an EXIF remover before sharing them separately.

A short checklist

• Order the pictures before you make the file.
• Choose A4 or Letter for printing, and same size for screens.
• Reduce very large photos first.
• Open the result and check each page.
• Keep the original pictures.

Sources

• JPEG (Wikipedia)
• PDF (Wikipedia)
• pdf-lib: create and modify PDF documents in any JavaScript environment