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PDF-XChange Viewer (now superseded by the PDF-XChange Editor) is a freemiumPDF reader for Microsoft Windows. It supports saving PDF forms (AcroForms) and importing or exporting form data in FDF/XFDF format. Since version 2.5, there has been partial support for XFA, and exporting form data in XML Data Package (XDP) or XML format. OCR support was also added in version 2.5.
Through its print driver, PDF files are able to be created from any Windows app that supports printing. Several PDF-related SDKs are available for developers. The following programming languages are supported: C++, C#, C, Visual Basic (classic), Visual Basic (modern), Delphi, and Clarion.
Its viewer is compatible with Wine, which provides another way to annotate PDFs on Linux.
List of PDF software