I was recently in a situation where I had to convert a stack of JPEG files to PDF. This was a job need. The human resources department of my to be employer had asked me for a number of forms. These forms had to be filled and sent only as PDF. I did not think there would be a problem because I have a PDF printer installed. I was wrong; it appears that files have to be 2MB or less in size.
I am unaware of any equation that equates image size to file size. I searched and found a few online converters which would shrink the file to the size I wanted. However, I wanted to avoid online services because these were sensitive documents.
The answer was in a thread on the stack exchange forums.
Image To PDF or XPS
This is a tiny program written in visual basic .net. It is fully accessible and converted my files seamlessly. There was no complex dragging with the mouse and all the processing by the program was done on the local computer.
The program is supplied without charge but there is a donate button on the about page which you may want to use.
In addition, unlike the PDF printer approach where I would open each image, print, enter the file name and then move on to the next file, I can add the images I want to convert and the program will do the rest. The program can either combine all images into a single PDF file or it can save the individual files in a folder you specify.
It does not need any installation so there are no pesky licenses to manage.
Please note, there is no specific option that asks you about file size. The program does its conversion and by default, produces small PDF files.
Finally, the program can be run from the command line which allows you to use the program in any scripts you may have.