add option to strip annotation (UglyToad#492)

* add option to strip annotation

* fix implementation and tests

---------

Co-authored-by: arne.hansen <arne.hansen@digitecgalaxus.ch>
Co-authored-by: Eliot Jones <elioty@hotmail.co.uk>

Author: 3 people

src/UglyToad.PdfPig.Tests/Writer/PdfDocumentBuilderTests.cs

@@ -129,6 +129,31 @@ public void CanFastAddPageAndStripLinkAnnots()
             }
         }
 
+        [Fact]
+        public void CanFastAddPageAndStripAllAnnots()
+        {
+            var first = IntegrationHelpers.GetDocumentPath("outline.pdf");
+            var contents = File.ReadAllBytes(first);
+
+            byte[] results = null;
+            using (var existing = PdfDocument.Open(contents, ParsingOptions.LenientParsingOff))
+            using (var output = new PdfDocumentBuilder())
+            {
+                output.AddPage(existing, 1, false);
+                results = output.Build();
+                var pg = existing.GetPage(1);
+                var annots = pg.ExperimentalAccess.GetAnnotations().ToList();
+                Assert.NotEmpty(annots);
+            }
+
+            using (var rewritten = PdfDocument.Open(results, ParsingOptions.LenientParsingOff))
+            {
+                var pg = rewritten.GetPage(1);
+                var annots = pg.ExperimentalAccess.GetAnnotations().ToList();
+                Assert.Empty(annots);
+            }
+        }
+
         [Fact]
         public void CanReadSingleBlankPage()
         {

src/UglyToad.PdfPig/Writer/PdfDocumentBuilder.cs

@@ -307,8 +307,9 @@ private sealed class PageInfo(DictionaryToken page, IReadOnlyList<DictionaryToke
         /// </summary>
         /// <param name="document">Source document.</param>
         /// <param name="pageNumber">Page to copy.</param>
+        /// <param name="keepAnnotations">Flag to set whether annotation of page should be kept</param>
         /// <returns>A builder for editing the page.</returns>
-        public PdfPageBuilder AddPage(PdfDocument document, int pageNumber)
+        public PdfPageBuilder AddPage(PdfDocument document, int pageNumber, bool keepAnnotations = true)
         {
             return AddPage(document, pageNumber, null);
         }
@@ -453,6 +454,11 @@ public PdfPageBuilder AddPage(PdfDocument document, int pageNumber, Func<PdfActi
 
                 if (kvp.Key == NameToken.Annots)
                 {
+                    if (!keepAnnotations)
+                    {
+                        continue;
+                    }
+                    
                     var val = kvp.Value;
                     if (kvp.Value is IndirectReferenceToken ir)
                     {