This fast and free OCR software extracts text from image files and PDF items.
Online OCR web app: https://ocr.a9t9.com/
Open-source Windows store app: http://blog.a9t9.com/p/free-ocr-software.html
The application is available as web service (online OCR) or as open-source Windows store app.
You can open an image or PDF file. The OCR conversion is fast and has a very good conversion quality.
Note that there is an older version for the Windows Desktop. It is also open-source but the conversion quality is not as good as it uses the somewhat outdated Tesseract OCR engine. Better use the new OCR web app or the Windows 8 store app.