GImageReader - gImageReader is a simple Gtk/Qt front-end to the Tesseract OCR Engine.

Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.

Adobe Scan - Scan anything into a PDF using your mobile device.

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Wondershare PDFelement - All-in-one PDF editor

Tesseract - Tesseract is an optical character recognition engine for various operating systems