Yes you should be able to use the OCR addon in Windows 7.  You can either get it by going to the NVDA menu, then tools then Manage add-ons then the "Get add-ons" button, or from: https://addons.nvda-project.org/index.en.html

The OCR add-on is available from this page: https://addons.nvda-project.org/addons/ocr.en.html

Essentially, once setup, move to the image or PDF file (open the PDF file in Adobe reader), etc, then press NVDA+r.  From there use the review cursor to read or copy the text which was found and press escape when done.

All the review cursor keyboard shortcuts are available from the User Guide: https://www.nvaccess.org/files/nvda/documentation/userGuide.html#ReviewingText

Alternatively they are in the Basic Training for NVDA module, which also has in-depth step by step activities to help you get familiar with them (not directly with OCR though).  The good news is that the section on the review cursor is in the free sample available from: 

(Electronic text, the sample is a web page link): https://www.nvaccess.org/product/basic-training-for-nvda-ebook/

(Audio, the sample is a single MP3 which will play in your browser or you can download it.  The full course is completely marked up with DAISY): https://www.nvaccess.org/product/basic-training-for-nvda-downloadable-audio/

Regards

Quentin.