If you’re creating PDFs for download as lead magnets, you’ll need an app for laying out pages.
Doing this on a mobile device is less than ideal and with few mobile options, using one of the online options may be the best choice available.
Using downloaded software, the quickest and easiest way to create a PDF is using LibreOffice Writer.
If you want a more sophisticated looking design, Scribus (https://www.scribus.net/) is a surprisingly powerful free option for Windows, Mac and Linux. I had my first experience of this years ago when it was much earlier in development, and it was an utter train wreck of an app.
It’s matured well now though and can create accomplished work. Someone used to working with Adobe Indesign will probably find themselves driven to tears at points, but anyone new to using such software should be more forgiving.
The weak point for Scribus is that it’s range of features means there’s a steep learning curve to get to grips with everything.
If you do find yourself tearing up too much using Scribus, Affinity Publisher (https://affinity.serif.com/en-us/publisher/) offers a more civilized experience for $50. It also comes with a steep learning curve
For Windows users only, Lunacy (https://icons8.com/lunacy) is also free app offered by Icons8. This looks a more user friendly option and should make it possible for most new users to make good looking multi-page PDFs.
If neither of those appeal, here’s a couple of online options that may be a better fit.
First is Google Docs (https://docs.google.com/). If you’re happy with a simpler design, Docs could be the quickest and easiest way to create one or more pages and save as a PDF. This is more flexible than most imagine and it has some preset templates you can choose from and tweak to your taste.
For a more polished result, Canva (https://www.canva.com/) is a popular choice with many. This is a freemium product, but the free account level should be fine for most users just starting out. Thanks to its popularity, you should easily find plenty of tutorials online to help create most anything you want.