Skip LinkAnnotations when collecting field objects (issue 19281)

The `/Root/AcroForm/Fields` array contains a "ridiculous" number of LinkAnnotations, which obviously makes no sense since those are not form fields.
To improve performance we'll thus ignore those when collecting the field objects.

src/core/document.js

@@ -20,6 +20,7 @@ import {
   info,
   InvalidPDFException,
   isArrayEqual,
+  objectSize,
   PageActionEventType,
   RenderingIntentFlag,
   shadow,
@@ -1775,6 +1776,13 @@ class PDFDocument {
     if (!(field instanceof Dict)) {
       return;
     }
+    let subtype = await field.getAsync("Subtype");
+    subtype = subtype instanceof Name ? subtype.name : null;
+    // Skip unrelated annotation types (see issue 19281).
+    switch (subtype) {
+      case "Link":
+        return;
+    }
     if (field.has("T")) {
       const partName = stringToPDFString(await field.getAsync("T"));
       name = name === "" ? partName : `${name}.${partName}`;
@@ -1890,9 +1898,12 @@ class PDFDocument {
             })
           );
         }
-
         await Promise.all(allPromises);
-        return { allFields, orphanFields };
+
+        return {
+          allFields: objectSize(allFields) > 0 ? allFields : null,
+          orphanFields,
+        };
       });
 
     return shadow(this, "fieldObjects", promise);
@@ -1915,7 +1926,7 @@ class PDFDocument {
     if (catalogJsActions) {
       return true;
     }
-    if (fieldObjects) {
+    if (fieldObjects?.allFields) {
       return Object.values(fieldObjects.allFields).some(fieldObject =>
         fieldObject.some(object => object.actions !== null)
       );

test/pdfs/issue19281.pdf.link

@@ -0,0 +1 @@
+https://github.com/user-attachments/files/18304780/Antarctica-Grid.pdf

test/test_manifest.json

@@ -11239,5 +11239,13 @@
     "link": true,
     "disableFontFace": true,
     "type": "eq"
+  },
+  {
+    "id": "issue19281",
+    "file": "pdfs/issue19281.pdf",
+    "md5": "c5db558965e4189cc6db2720cdaa3e55",
+    "rounds": 1,
+    "link": true,
+    "type": "other"
   }
 ]

test/unit/api_spec.js

@@ -1713,6 +1713,20 @@ describe("api", function () {
       await loadingTask.destroy();
     });
 
+    it("gets fieldObjects and skipping LinkAnnotations", async function () {
+      if (isNodeJS) {
+        pending("Linked test-cases are not supported in Node.js.");
+      }
+
+      const loadingTask = getDocument(buildGetDocumentParams("issue19281.pdf"));
+      const pdfDoc = await loadingTask.promise;
+      const fieldObjects = await pdfDoc.getFieldObjects();
+
+      expect(fieldObjects).toEqual(null);
+
+      await loadingTask.destroy();
+    });
+
     it("gets non-existent calculationOrder", async function () {
       const calculationOrder = await pdfDocument.getCalculationOrderIds();
       expect(calculationOrder).toEqual(null);