A free program for Android, by Extras Studeio.

Doc Scanner is an application for scanning and saving files in PDF format. The app is based on an internal camera of the device. You can take a photo, select a page from a PDF file, crop it, add a watermark, and save it in the history.

You can share your PDFs via email, or upload them to Dropbox, Google Drive, or OneDrive. You can also share them on Facebook, Twitter, WhatsApp, or any other social media. 

Doc Scanner is a free, offline application. You do not need to pay any kind of subscription fees. You can download the app from Google Play Store.