Short answer
To merge several JPG or PNG images into a single PDF, add them all at once — each image becomes one page, in the order you add them. Choose a page size, then download the one combined PDF. It's done in your browser, so nothing is uploaded.
This is the fastest way to package a set of photos — receipts, a multi-page scan, product shots — into one shareable, printable file. There's no page limit beyond your device's memory, and you can mix JPG and PNG.
Because pages follow the order you add the images, add them in the sequence you want, or add them in batches to control ordering.
There's no fixed limit — it depends on your device's memory. Dozens of typical phone photos combine without trouble because the work happens locally in your browser.
Yes. Each image becomes a page in the order you add it, so add them in the sequence you want them to appear.