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Warning about PDFium.DLL

Author: tothpaul

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+# Binary distribution
+
+you can use the [source code](https://github.com/tothpaul/PDFiumReader/tree/master/src) to rebuild PDFiumReader.exe
+
+## About PDFiumReader.exe
+
+it's a Release version of the provided source code compiled with Delphi Tokyo 10.2.1 for Win32
+
+## About PDFium.DLL
+
+the provided DLL is a copy of a 2016 version from [PDFiumViewer](https://github.com/pvginkel/PdfiumViewer/tree/master/Libraries/Pdfium)
+
+you should not use this version in production, it is provided only for testing purpose.
+
+I'm not a C++ guy, so I will not try to compile a new version of this DLL.
+
+More info on PDFium on [googlesource.com](https://pdfium.googlesource.com/pdfium/)