What are some free PDF apps I can use to manage and reduce file sizes?

The community suggests several free applications and methods to manage PDF files without incurring costs. Key recommendations include using online services like iLovePDF for editing and compressing files, Adobe Acrobat's trial version, and utilizing built-in tools on Mac, such as Preview, which allows for PDF editing and size reduction. For iPhone users, there's a method to scan documents into PDF format through the Files app. Additionally, Pdfsam is highlighted as a good tool for combining and splitting PDF files.