Images to PDF: Fit-to-Image vs A4, and Why HEIC Gets Rejected

Receipts, screenshots, scanned IDs — sooner or later someone asks for "one PDF please". The Image to PDF Converter merges images into a single document without re-compressing them, and the interesting decisions are all about page geometry.

Choose the page mode deliberately

Fit-to-image creates pages exactly matching each image's pixel size. One screenshot per page, no borders, no scaling artifacts — the right choice when images share dimensions (documentation captures, slide exports).

A4/Letter centers each image on a fixed page with a margin you control. Auto-rotate turns landscape images on their side so they use the paper properly — rotating the page, not the image, keeps every pixel upright and undistorted.

The sizing logic is a simple max-fit: scale = min(available width ÷ image width, available height ÷ image height), centered on the page. No aspect ratio is ever bent.

Quality is preserved by construction

Images are embedded with pdf-lib at their original resolution — the PDF is a container around your exact JPEG/PNG bytes. There is no decode-reencode step, so file size grows by roughly the sum of the inputs and nothing else.

The HEIC question

iPhone photos in HEIC are politely rejected with a clear message rather than a broken page, for a boring reason: browser Canvas and pdf-lib have no free HEIC codec on most platforms, and silently producing a blank page would be worse than an honest refusal. Convert to JPG first (any photo app does), then merge. Reordering is drag-free — up/down buttons per image — and the order you see is the page order you get.

When to use what

Screenshots and same-size series → fit-to-image. Mixed photos for printing or expense bundles → A4 with margin. Coming back from PDF-land? The PDF to Image Converter reverses the trip, and PDF Tools splits or merges existing PDFs.