How can I convert JPG into PDF easily?
Never forget your little fellow Automator, sitting in a hard drive near you :)

Launch Automator, create a new workflow. Now you need to add two actions:


In the "Files &amp; Folders" select Ask for Finder Items and drag it. 
In the PDFs Category, find "New PDF from Images" and also drag it.


Your workflow should look like this:



Now read the options for each Action and customize accordingly. Investigate similar actions (especially in the Files &amp; Folders category) and perhaps the Photos if you want to transform your images from JPG to something else. In fact, go ahead and look all over automator, there are a lot of interesting things there. :)

When you're satisfied with your Workflow, click "Run" on the top right corner. Watch the magic happens and depending upon the number of items and your CPU power, you might go grab a coffee/tea.