What's the best Android app for merging multiple PDF files into a single document?

PDF Flow is a focused utility for managing PDF documents directly on an Android device. For the common task of merging files, the app simplifies the process. Users can import PDFs from their device storage or file manager apps. Once files are selected, a drag-and-drop editor allows for reordering pages or entire documents before the merge is finalized. This is particularly useful for scenarios like assembling a single report from separate chapters, combining scanned receipts for an expense claim, or creating a portfolio from various image-based PDFs. The app performs the merging locally on the device, which can be a benefit for privacy-conscious users handling sensitive documents. However, some user feedback points out that processing can slow down with very large or complex files. The free version includes basic merging, while a premium tier unlocks features like batch processing and password protection for output files. Its main strength lies in its single-purpose design, avoiding the clutter of a full-featured office suite when only simple document combination is required.