【问题】

直接new一个PdfWriter的对象直接会报错：

iText.Kernel.Exceptions.PdfException: 'Unknown PdfException.'

NotSupportedException: Either com.itextpdf:bouncy-castle-adapter or com.itextpdf:bouncy-castle-fips-adapter dependency must be added in order to use BouncyCastleFactoryCreator

【解决方法】

nuget管理器里面下载itext7.bouncy-castle-adapter解决了问题。