IronPDF - SDK for creating and editing PDFs.
PdfPig - Read and extract text and other content from PDFs in C# (port of PDFBox)
Apache PDFBox - The Apache PDFBox™ library is an open source Java tool for working with PDF documents.
Document .Net - Gives you API to do everything with a document in PDF, DOCX, DOC, RTF, HTML and Text formats.
Qoppa jPDFFields - Use jPDFFields Java PDF SDK to work with interactive PDF forms in both AcroForm and XFA formats.
PDFSharp - Office & Productivity and Development