Error: The type 'System.IO.Packaging.Package' is defined in an assembly that is not referenced.

Using OpenXml.

The type 'System.IO.Packaging.Package' is defined in an assembly that is not referenced. You must add a reference to assembly 'WindowsBase, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.

---solutions---

Add WindowsBase.dll in 'Add Reference' -> .NET tab

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原文地址：https://www.cnblogs.com/vincentDr/p/2872826.html