diff --git a/itext.tests/itext.sign.tests/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest.cs b/itext.tests/itext.sign.tests/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest.cs
index 2b444482d5..9db676ffe2 100644
--- a/itext.tests/itext.sign.tests/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest.cs
+++ b/itext.tests/itext.sign.tests/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest.cs
@@ -468,6 +468,43 @@ public virtual void TaggedDocRemoveStructTreeElementTest(bool continueValidation
             }
         }
 
+        [NUnit.Framework.TestCaseSource("CreateParameters")]
+        public virtual void AnnotationModificationAllowedTabsChangesTest(bool continueValidationAfterFail) {
+            SetUp(continueValidationAfterFail);
+            using (PdfDocument document = new PdfDocument(new PdfReader(SOURCE_FOLDER + "annotationModificationAllowedTabsChangesTest.pdf"
+                ))) {
+                DocumentRevisionsValidator validator = builder.BuildDocumentRevisionsValidator();
+                ValidationReport report = validator.ValidateAllDocumentRevisions(validationContext, document);
+                AssertValidationReport.AssertThat(report, (a) => a.HasStatus(ValidationReport.ValidationResult.VALID).HasNumberOfLogs
+                    (0));
+            }
+        }
+
+        [NUnit.Framework.TestCaseSource("CreateParameters")]
+        public virtual void AnnotationModificationNotAllowedTabsChangesTest(bool continueValidationAfterFail) {
+            SetUp(continueValidationAfterFail);
+            using (PdfDocument document = new PdfDocument(new PdfReader(SOURCE_FOLDER + "annotationModificationNotAllowedTabsChangesTest.pdf"
+                ))) {
+                DocumentRevisionsValidator validator = builder.BuildDocumentRevisionsValidator();
+                ValidationReport report = validator.ValidateAllDocumentRevisions(validationContext, document);
+                AssertValidationReport.AssertThat(report, (a) => a.HasStatus(ValidationReport.ValidationResult.INVALID).HasNumberOfFailures
+                    (1).HasLogItem((l) => l.WithCheckName(DocumentRevisionsValidator.DOC_MDP_CHECK).WithMessage(DocumentRevisionsValidator
+                    .TABS_MODIFIED).WithStatus(ReportItem.ReportItemStatus.INVALID)));
+            }
+        }
+
+        [NUnit.Framework.TestCaseSource("CreateParameters")]
+        public virtual void AnnotationModificationNotAllowedTabsSetToDefaultTest(bool continueValidationAfterFail) {
+            SetUp(continueValidationAfterFail);
+            using (PdfDocument document = new PdfDocument(new PdfReader(SOURCE_FOLDER + "annotationModificationNotAllowedTabsSetToDefaultTest.pdf"
+                ))) {
+                DocumentRevisionsValidator validator = builder.BuildDocumentRevisionsValidator();
+                ValidationReport report = validator.ValidateAllDocumentRevisions(validationContext, document);
+                AssertValidationReport.AssertThat(report, (a) => a.HasStatus(ValidationReport.ValidationResult.VALID).HasNumberOfLogs
+                    (0));
+            }
+        }
+
         [NUnit.Framework.TestCaseSource("CreateParameters")]
         public virtual void OutlinesNotModifiedTest(bool continueValidationAfterFail) {
             SetUp(continueValidationAfterFail);
diff --git a/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationAllowedTabsChangesTest.pdf b/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationAllowedTabsChangesTest.pdf
new file mode 100644
index 0000000000..9db70e7eee
Binary files /dev/null and b/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationAllowedTabsChangesTest.pdf differ
diff --git a/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationNotAllowedTabsChangesTest.pdf b/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationNotAllowedTabsChangesTest.pdf
new file mode 100644
index 0000000000..95a551a793
Binary files /dev/null and b/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationNotAllowedTabsChangesTest.pdf differ
diff --git a/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationNotAllowedTabsSetToDefaultTest.pdf b/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationNotAllowedTabsSetToDefaultTest.pdf
new file mode 100644
index 0000000000..a29f030a66
Binary files /dev/null and b/itext.tests/itext.sign.tests/resources/itext/signatures/validation/DocumentRevisionsValidatorIntegrationTest/annotationModificationNotAllowedTabsSetToDefaultTest.pdf differ
diff --git a/itext/itext.sign/itext/signatures/validation/DocumentRevisionsValidator.cs b/itext/itext.sign/itext/signatures/validation/DocumentRevisionsValidator.cs
index 68df7c62b9..20f9ffb19a 100644
--- a/itext/itext.sign/itext/signatures/validation/DocumentRevisionsValidator.cs
+++ b/itext/itext.sign/itext/signatures/validation/DocumentRevisionsValidator.cs
@@ -152,6 +152,10 @@ public class DocumentRevisionsValidator {
         internal const String PAGE_MODIFIED = "Page was unexpectedly modified.";
 //\endcond
 
+//\cond DO_NOT_DOCUMENT
+        internal const String TABS_MODIFIED = "Tabs entry in a page dictionary was unexpectedly modified.";
+//\endcond
+
 //\cond DO_NOT_DOCUMENT
         internal const String PERMISSIONS_REMOVED = "Permissions dictionary was removed from the catalog.";
 //\endcond
@@ -1510,15 +1514,21 @@ private bool ComparePages(PdfDictionary prevPages, PdfDictionary currPages, Vali
                     previousPageCopy.Remove(PdfName.Annots);
                     previousPageCopy.Remove(PdfName.Parent);
                     previousPageCopy.Remove(PdfName.StructParents);
+                    previousPageCopy.Remove(PdfName.Tabs);
                     PdfDictionary currentPageCopy = new PdfDictionary(currentKid);
                     currentPageCopy.Remove(PdfName.Annots);
                     currentPageCopy.Remove(PdfName.Parent);
                     currentPageCopy.Remove(PdfName.StructParents);
+                    currentPageCopy.Remove(PdfName.Tabs);
                     if (!ComparePdfObjects(previousPageCopy, currentPageCopy, usuallyModifiedObjects) || !CompareIndirectReferencesObjNums
                         (previousKid.Get(PdfName.Parent), currentKid.Get(PdfName.Parent), report, "Page parent")) {
                         report.AddReportItem(new ReportItem(DOC_MDP_CHECK, PAGE_MODIFIED, ReportItem.ReportItemStatus.INVALID));
                         return false;
                     }
+                    if (!CompareTabs(previousKid.GetAsName(PdfName.Tabs), currentKid.GetAsName(PdfName.Tabs))) {
+                        report.AddReportItem(new ReportItem(DOC_MDP_CHECK, TABS_MODIFIED, ReportItem.ReportItemStatus.INVALID));
+                        return false;
+                    }
                     PdfArray prevNotModifiableAnnots = GetAnnotsNotAllowedToBeModified(previousKid);
                     PdfArray currNotModifiableAnnots = GetAnnotsNotAllowedToBeModified(currentKid);
                     if (!ComparePageAnnotations(prevNotModifiableAnnots, currNotModifiableAnnots, report)) {
@@ -1533,6 +1543,13 @@ private bool ComparePages(PdfDictionary prevPages, PdfDictionary currPages, Vali
             return true;
         }
 
+        private bool CompareTabs(PdfName previousTabs, PdfName currentTabs) {
+            if (GetAccessPermissions() == AccessPermissions.ANNOTATION_MODIFICATION) {
+                return true;
+            }
+            return Object.Equals(previousTabs, currentTabs) || (previousTabs == null && currentTabs.Equals(PdfName.S));
+        }
+
         private void CollectRemovedAndAddedAnnotations(PdfArray previousAnnotations, PdfArray currentAnnotations) {
             ValidationReport dummyReport = new ValidationReport();
             IList<PdfDictionary> prevAnnots = new List<PdfDictionary>();
diff --git a/port-hash b/port-hash
index 31eca6a608..82e8c5e5ee 100644
--- a/port-hash
+++ b/port-hash
@@ -1 +1 @@
-8d4fbb6308e2126af33891bf5ad981ec9f2fd81b
+ce35dbce51bd8c3f1b01e78313f1f5a2a02201ff