NAPS2 (Not Another PDF Scanner 2) is my favorite opensource scanner software on Windows: http://naps2.sourceforge.net/
Scan documents to PDF and other file types, as simply as possible.
NAPS2 is a document scanning application with a focus on simplicity
and ease of use. Scan your documents from WIA- and TWAIN-compatible
scanners, organize the pages as you like, and save them as PDF, TIFF,
JPEG, PNG, and other file formats. Requires .NET Framework 4.0 or