JPG to PDF

Each image becomes a page. The picture is embedded as it is, at its original resolution, and placed on the page rather than redrawn, so nothing is resampled and nothing is lost.

Everything happens inside this page. Your file is read by JavaScript running on your own machine, and no part of it is sent anywhere.

Fit to image, or fit to paper

Fit to image makes every page exactly the size of the picture on it. Nothing is cropped, there are no borders, and a document of mixed photographs ends up with pages of different sizes. This is the right choice for anything that will be read on a screen.

A4 or Letter gives every page the same size and centres the image inside it with the margin you set. This is what you want if the document is going to be printed or filed, because a printer and a binder both expect one page size.

Orientation

Automatic looks at each picture and gives it a landscape page if it is wider than it is tall. That handles a folder of mixed photographs without you deciding page by page.

Force portrait or landscape when the document has to be consistent, and accept that some images will sit smaller on the page as a result.

File size, and what to do about it

A PDF made from photographs is large because photographs are large. Ten pictures from a modern phone camera will produce something between twenty and eighty megabytes, and nothing about the PDF wrapper changes that.

If the result needs to be emailed, compress the images before converting rather than after. A phone photo of a document at full resolution carries far more detail than the page needs, and reducing it before it becomes a page is both faster and better looking than squeezing the PDF afterwards.

This does not make the text searchable

A photograph of a page is a picture of text, not text. The words in it cannot be searched, selected or copied, and that is true of every tool that turns images into PDFs, not just this one.

Making them searchable needs OCR, which reads the shapes and writes an invisible text layer underneath. That is a different operation and it is worth doing on anything you will need to find again.