PDFBOX-3330: add information about removed PDUnknownField class in Migration Guide
diff --git a/content/2.0/migration.md b/content/2.0/migration.md
index 8100370..730e665 100644
--- a/content/2.0/migration.md
+++ b/content/2.0/migration.md
@@ -221,6 +221,9 @@
As form fields do support multiple annotations `PDField.getWidget()` has been removed in favour of `PDField.getWidgets()`which returns all
annotations associated with a field.
+#### PDUnknownField removed ####
+The `PDUnknownField` class has been removed, such fields are treated as `null` [see PDFBOX-2885](https://issues.apache.org/jira/browse/PDFBOX-2885).
+
### Document Outline
The method `PDOutlineNode.appendChild()` has been renamed to `PDOutlineNode.addLast()`. There is now also a complementary method `PDOutlineNode.addFirst()`.
