PDF-XChange Viewer is a free PDF reader for Microsoft Windows. The basic reader, which can be downloaded free of charge, includes extended/markup capabilities such as typing, highlighting, callouts, and notes. Another useful features is the ability of displaying PDF files in the "preview" pane of the Windows Explorer without locking the file (and thus allowing for easy setting of metadata info). An advanced paid version is also available.
It supports saving of filled PDF forms (AcroForms) and import/export of form data in FDF/XFDF format. It added OCR support as of version 2.5.
PDF-XChange Lite print driver is a print driver enabling the creation of PDFs from Microsoft Windows applications. It is free for academic and home use. Also available is PDF-XChange Standard, which brings advanced PDF creation options.
A related product is PDF-Tools, which allows creation and manipulation of PDFs from a variety of sources including images, text documents, etc. Batch conversion capabilities with filename macros are included.
Finally, a number of PDF-related SDKs for developers are available, including PDF Tools SDK, PDF-XChange Viewer SDK, PDF-XChange Drivers SDK, and Image SDKs. These allow creation, manipulation, reading, writing, OCR, search, and display of PDFs; and multi-language support (C++, C#, C, VB, VB.NET, Delphi, Clarion) is available.
PDF-XChange Viewer works under Wine, providing another way to annotate PDFs under Linux.