PDF Clown - PDF Clown is an open-source general-purpose library for manipulating PDF documents through multiple abstraction layers, rigorously adhering to PDF 1.7 Specification

jOfficeConvert - Use jOfficeConvert Java PDF SDK to convert MS Word and Excel documents to PDF or images, or print documents automatically from your Java applications.

Document .Net - Gives you API to do everything with a document in PDF, DOCX, DOC, RTF, HTML and Text formats.

Excel Merger - Excel Merger is a free software tool that merges Excel files and workbooks into one single Excel file or workbook without installing MS Office or Excel.

PDFSharp - Office & Productivity and Development

Birdie XLSX to XLS Converter - Convert huge bundles of XLSX files to XLS by using the batch mode conversion option of XLSX to LXS Converter.