QUICK ANSWERStart with the tool that matches your immediate input.
Open Compare PDF Files first when its stated purpose matches the result you need now. Use Merge PDF only when it solves a separate next task.
This guide is for students, office teams, administrators, and document-heavy workflows. Start with Compare PDF Files when your immediate task is to use the Compare PDF Files to complete this file task privately in your browser. Move to Merge PDF only when you also need to use the Merge PDF to complete this file task privately in your browser.
The goal is not to run two tools automatically. It is to finish the first narrow task, inspect its result, and then decide whether Merge PDF solves a genuinely different next step.
Both tools sit in PDF Tools, but they handle different inputs or outcomes. Keeping those roles separate reduces repeated work and makes verification easier.