4-Step Computer Security Upgrade
Learn to encrypt your files, secure your computer when using public Wi-Fi, enable two-factor authentication, and use good passwords.
But this list includes tools for appending and subtracting pages from PDF files, creating interactive PDF documents (with amazing open-source publishing tool Scribus), and annotating PDF documents.
Take advantage of the great resources out there. And if you use an open source application, contribute to the project to keep it going!