If you’re an advocate for open-source tools and prioritize privacy, Penpot is your best bet, especially if you work collaboratively with designers and developers. Its real-time collaboration features and compatibility with open standards make it ideal for teams that are comfortable with a less polished experience. However, if you require extensive plugins and a mature ecosystem, it may not suffice.
On the other hand, if your focus is on secure, high-volume PDF processing, Stirling-PDF is the superior choice. Its capabilities are tailored for businesses that handle sensitive documents. Just keep in mind that while it offers a free tier, the costs can escalate with heavy usage, and it lacks a robust mobile app. Avoid it if you need a fully-featured mobile experience or wish to keep costs down with a completely free solution.