How to convert JPG images to PDF

Building a PDF out of pictures is quick. The part people do not expect is that the picture decides how big the page is — so it is worth knowing before you send the file to a printer.

What actually goes into the file

Each image becomes one page, in the order you added them. A JPG is embedded as a JPG and a PNG as a PNG — byte for byte, with no re-encoding — so nothing is re-compressed and no quality is lost on the way in. That also means the PDF is about as heavy as the images were.

Anything that is neither PNG nor JPG — WEBP, HEIC, a screenshot saved in an unusual format — is decoded first and re-saved as a JPEG at 92% quality. Two consequences: transparency is lost (the image is flattened onto white), and there is one small, one-time loss of quality. If the images matter, convert them to PNG or JPG first.

The page size is decided by the picture, not by you

There is no A4 or Letter option, because the tool does something simpler and more literal: each page is created at the image's own pixel size, measured in points (1/72 inch). A 3000 x 4000-pixel photo therefore becomes a page about 106 x 141 cm. Nothing is distorted — the proportions are exact — but a photograph makes a poster-sized page rather than a document page.

That is fine for a set of screenshots you want to keep sharp, and awkward for anything going to a printer that expects A4. If you need document-sized pages, resize the images before converting. The numbers worth remembering are the paper sizes in pixels: A4 at 150 dpi is about 1240 x 1754, and at 300 dpi about 2480 x 3508. Resize to one of those and the pages come out exactly A4 — and the file becomes far smaller at the same time.

Making it smaller, and getting the order right

A PDF built from photos is heavy, and there is no way around that at conversion time — the images go in as they are. The real lever is the pixel count, and it works in your favour: halving the width and height of an image removes about three quarters of the data. Resizing a 4000-pixel photo to 1240 pixels before converting is the difference between a 6 MB page and a 0.5 MB one, with no visible change on screen.

If you have already built the file and it is too big, compression is the next step — the strong level re-renders each page as a smaller image, which is exactly what a photo-heavy document needs.

Order is simply the order you add the images. When there are more than nine, the filesystem's own sorting is what trips people up: photo_10 sorts before photo_2 unless the numbers are padded. Renaming to photo_01, photo_02 ... photo_10 before you add them takes a minute and saves rearranging the document afterwards.

Questions

Can I mix PNG and JPG in the same PDF?

Yes, and each one keeps its own format inside the file: PNGs stay PNGs and JPGs stay JPGs. Only the other formats (WEBP, HEIC and so on) are converted, to JPEG.

How do I control the page size?

You do not set it directly — the image does. Each page is created at the image's pixel size measured in points, so a 3000-pixel-wide photo becomes a page about 3000 points (roughly 105 cm) wide. If you need A4 pages, resize the images first: about 1240 x 1754 pixels is A4 at 150 dpi, and 2480 x 3508 is A4 at 300 dpi.

Can I put several photos on one page?

Not in this tool — one image per page. If you need two or four to a sheet, put them side by side in one image first (any photo editor can do it) and convert that.

Why is the PDF so large?

Because the images are embedded as they were. JPEGs are already compressed, so the PDF cannot shrink them further. A modern phone photo is 3-8 MB, so twenty of them make a file of 60-160 MB. Compression is the tool for that, not conversion.

Some of my photos came out sideways. Why?

Phone cameras often store the picture unrotated and add a note saying which way up it is. A JPG is embedded exactly as it is stored, and a PDF viewer does not read that note, so the image can land the wrong way up. Rotate or re-save the photo in a photo editor first, and it will be right in the PDF.

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