Partial fox for future possible porting to .NET Standard

Author: Snipx

itext/itext.cleanup/itext/pdfcleanup/CleanUpExtensions.cs

@@ -45,6 +45,7 @@ source product.
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Reflection;
 using System.Text;

itext/itext.cleanup/itext/pdfcleanup/PdfCleanUpTool.cs

@@ -189,7 +189,7 @@ public PdfCleanUpTool(PdfDocument pdfDocument, bool cleanRedactAnnotations) {
         private static Type GetClass(string className)
         {
             String licenseKeyClassFullName = null;
-            Assembly assembly = typeof(PdfCleanUpTool).Assembly;
+            Assembly assembly = typeof(PdfCleanUpTool).GetAssembly();
             Attribute keyVersionAttr = assembly.GetCustomAttribute(typeof(KeyVersionAttribute));
             if (keyVersionAttr is KeyVersionAttribute)
             {