The online editor allows for "light" editing of existing PDFs. While it doesn't offer the deep paragraph reflow of a word processor, it is perfect for adding essential elements.
PDF24 Tools (tools.pdf24.org) is a comprehensive, free browser-based suite developed by Geek Software GmbH that offers over 30 PDF utilities without requiring accounts or installations. The platform includes essential features like merging, splitting, compressing, and converting files, with a focus on privacy through encrypted transfers and automatic file deletion. For more information, visit tools.pdf24.org.