It happens more often these days. You get some form sent to you as a PDF. You print it out, and fill it in, and then you want to scan it back in and send it back. For one reason or another, my scanner likes to scan documents to JPEG files: one file per scan. Grr... 

In the past, I've used some PDF printer driver or other to solve this problem, but under the water they pretty much all use ghostscript, so why not do it directly. I used to install cygwin on my Windows machines to get access to utilities like this, but these days, Windows embeds a pretty much functional Ubuntu. 

So yeah - just directly using ghostscript. How hard can it be? Well it turns out that a bit of Googling leads you to typing some pretty gnarly command lines, especially since I had scanned a 15 page document into 15 separate JPG files. And then Adobe Acrobat didn't understand the resulting document. No good at all. So then I googled further and found this. 

It turns out that by installing not only ghostscript but imagemagick, the imagemagick "convert" utility knows how to do exactly what you want, presumably by enlisting the help of ghostscript. So simply by cd'ing to the directory where I had my scans, this...

$ convert *.JPG outputfile.pdf

... did the trick. Pretty neat, huh? Note to self....