Why one PDF beats twelve photos
Most forms, claims portals and email threads want a single document. Sending a dozen separate images means the recipient has to open each one, and many upload forms only accept one file at a time. Merging them keeps the order you intended and travels as one attachment.
Page size and margins
Fitting each page to its image is usually right for photographs, because nothing is cropped and no white space is added. Choose A4 or Letter when the result will be printed, or when a form specifically asks for a standard page size.
Margins matter mainly for printing, since most printers cannot reach the very edge of the paper. For screen use, none is fine.
iPhone photos
iPhones save in HEIC by default. This tool converts them for you as it works, so you can mix HEIC and JPG freely in the same document. The decoder is only downloaded if you actually include a HEIC file. If you would rather convert them separately first, the HEIC to JPG converter does that on its own.
If the finished PDF is still too large
Photographs are the reason PDFs get big, so the quality and downscale settings above usually solve it. When they do not, or when you are combining pages from a scan you already have, the PDF compressor takes a finished document and squeezes it to a size you specify.
Going the other way, the PDF to JPG tool pulls the pages back out as separate pictures, which is useful when a form wants images rather than a document.
Getting a scan that looks like a scan
Most people building a PDF from photographs are photographing documents rather than scenery, and a few habits make an enormous difference. Shoot in even, indirect light rather than under a single overhead bulb, which casts a shadow from your own hand. Fill the frame with the page so the detail is in the paper rather than the table around it. Hold the phone parallel to the page instead of at an angle, since perspective distortion cannot be undone here.
If the document has text you will need to read later, choose 2200 or 3000 pixels rather than 1600. Text tolerates far less compression than photographs do before it starts to look furry.
Page order and orientation
Photos arrive in whatever order your device lists them, which is often alphabetical by filename rather than the order you took them. The arrows beside each file let you fix that before creating the document, and the numbers on the left show exactly what page each image will become.
When fitting pages to their images, portrait and landscape photographs each produce a page of matching shape, so a mixed batch gives you a document with pages of differing sizes. That is fine on screen but awkward to print. Choosing A4 or Letter instead gives every page the same dimensions, with each image centred inside it.
Why file size matters more than it seems
Twelve photographs straight from a modern phone total roughly 60MB. Assembled without downscaling, the PDF will be about the same, and no email or upload form will take it. Reducing the longest side to 2200 pixels keeps the document perfectly readable while cutting it to a few megabytes.
The default settings above are chosen to produce a document that looks right on screen and prints acceptably, while staying small enough to send. Raise them only if you know the pages will be printed at full size.
What this cannot do
The result is a document containing pictures, so the text inside it is not selectable or searchable. Making a photographed page searchable requires optical character recognition, which reads the letters and stores them separately, and that is a different job to this one.
If you need searchable text, most phone scanner apps perform recognition as they capture. Use one of those for documents you will need to search later, and this tool for everything else.
Questions
Can I change the order?
Yes. Use the arrows beside each file to move it up or down before creating the PDF.
Are my photos uploaded?
No. The PDF is assembled in your browser. That matters for the things people usually combine into a PDF, which tend to be receipts, ID documents and medical paperwork.
Why is my PDF large?
Photographs contain far more detail than a page can display. Lower the quality slider or downscale to 1600 pixels, and the file will shrink dramatically with no visible difference on screen.