PDF Mergy

This app lets you merge or compress PDF files while keeping your documents private. Everything runs locally in your browser, so your files are processed on your device and never uploaded to a server. Select PDFs from your computer or import them from Google Drive™, then drag and drop to set the order. The merged PDF is created exactly in the sequence you see on screen.

Open PDFs straight from your file manager: choose "Open with" and PDF Mergy.