PdfPig - Read and extract text and other content from PDFs in C# (port of PDFBox)
PDFSharp - Office & Productivity and Development
iTextPDF - iText offers flexible tools for PDF creation, editing and inspection.
ABCpdf.NET - ABCpdf.NET is a high-profile and powerful PDF Library that delivers the best experience possible for everyone.
Wicked PDF - PDF generator (from HTML) plugin for Ruby on Rails
PDFJet - PDFJet is a mobile and cloud PDF Library for Java and .NET to generate PDF documents.