Two jobs on one page
This page does two specific things. It turns iPhone HEIC photos into JPG, and it combines any set of images into a single PDF. It accepts JPG, PNG, WebP and HEIC together in one drop, tags each card as HEIC or by its type, and enables the HEIC to JPG button only when at least one HEIC file is present. For every other pair of formats, the site has a dedicated converter; PNG to JPG, WebP to PNG and the rest use the WebAssembly encoder and are listed on the home page.
HEIC to JPG, and why it is slower than the other converters
HEIC is the container Apple uses for photos on iPhone and iPad since iOS 11. It stores an image compressed with HEVC, which is roughly twice as efficient as JPEG, so a 12 megapixel shot is about 1.5 to 2 MB instead of 3 to 4. The problem is that Windows, many Android apps, older Macs, web forms and most content management systems cannot open it. Browsers cannot decode HEIC natively either, which is why this page loads the heic2any library on demand; it decodes the HEVC stream in JavaScript and WebAssembly and re-encodes the result as JPEG at quality 0.9.
That decode is heavy. Expect 2 to 6 seconds per photo on a laptop and noticeably longer on a phone, versus a fraction of a second for a PNG to JPG conversion. The output is a normal JPG that opens everywhere, typically 2.5 to 4 MB for a 4032x3024 photo, larger than the HEIC because JPEG is the less efficient codec and 0.9 is a high quality setting. Run the result through compress if the size matters. Metadata, including GPS and the capture date, is not carried into the JPG. A HEIC that holds several images, such as a burst, converts as its first image. If the file is a HEIF from a non-Apple camera using an unusual profile, decoding may fail, and the card reports the error instead of silently producing a blank image. For background on the format see what is HEIC.
Combining images into a PDF
Combine into PDF builds the document with jsPDF, one page per image, in the order the files were dropped. Each page takes the pixel dimensions of its image, so a 1080x1920 screenshot becomes a portrait page and a 1920x1080 one becomes a landscape page, with no scaling, no margins and no white borders. HEIC files are converted to JPEG on the fly before being placed. Inside the PDF every image is stored as JPEG at quality 0.92, whatever the source was, so a transparent PNG is flattened onto black by the canvas step and a lossless PNG becomes lossy on the page. The download is always named images.pdf.
Size scales with page count. Ten phone photos usually give a 15 to 25 MB PDF; ten screenshots of a web page come in around 2 to 5 MB. Compress the photos first if the PDF has to fit an email attachment limit.
What this PDF is not
The PDF is a stack of pictures. It has no text layer, so you cannot search it or select words, and screen readers see nothing. If the images are scans or screenshots of documents and you need the words, run them through image to text first and keep the extracted text alongside the PDF. There is also no page reordering after the drop; if the order is wrong, reload the page and drop the files again in the right sequence. Everything is generated in the browser, nothing is uploaded, and a batch of a few dozen photos is comfortable on any laptop.