Overview
Paint.NET is primarily programmed in the C# programming language. Its native image format, .PDN, is a compressed representation of the application's internal object format, which preserves layering and other information. Excluding the installer, text, and graphics, Paint.NET was released under a modified version of the MIT License. It was initially released as completely open source, but due to breaches of license, all resource files (such as interface text and icons) were released under a Creative Commons license forbidding modification, and the installer was made closed-source.
Version 3.36 was initially released as partial open source, but the sources were later removed by Brewster, citing problems with plagiarism. In version 3.5, the license was altered to reflect this, and users are now prohibited from modifying the software. As free licenses cannot be revoked, developers can still legally develop forks based on version 3.36 and earlier. However, unlike most proprietary software licenses, the new license allows users to decompile and reverse engineer the software, provided that no modifications are made.
Brewster later stated that he hopes to release portions of the source code back into the public.
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