PDFEncrypt is a free, open-source app that allows you to encrypt PDF files without purchasing expensive software.
About The App
PDFEncrypt is a free, open-source utility to encrypt PDF files using standard PDF encryption algorithms. When a document is encrypted, its contents become unreadable. An authorized user can decrypt the document to obtain access to the contents. If a PDF document is encrypted with a password, the user must specify the password before the document can be viewed in Adobe Reader or Adobe Acrobat.
PDFEncrypt provides a means to encrypt any standard PDF document for free, without the need to purchase the Adobe Acrobat software or upload your confidential PDF files to a third-party server for encryption. The app runs directly on your Windows PC and allows you to specify a password (required to open the document) as well as many options and permissions to apply to the PDF file.
This app uses the iTextPDF open source library for encryption operations, and is released under the AGPL license. Complete source code is available on GitHub, and you can download the installer for Windows 7, 8 and 10 below.