Display widget signature

- but don't validate them for now;
  - Firefox will display a bar to warn that the signature validation is not supported (see https://bugzilla.mozilla.org/show_bug.cgi?id=854315)
  - almost all (all ?) pdf readers display signatures;
  - validation is done in edge but for now it's behind a pref.

src/core/annotation.js

@@ -126,6 +126,8 @@ class AnnotationFactory {
             return new ButtonWidgetAnnotation(parameters);
           case "Ch":
             return new ChoiceWidgetAnnotation(parameters);
+          case "Sig":
+            return new SignatureWidgetAnnotation(parameters);
         }
         warn(
           `Unimplemented widget field type "${fieldType}", ` +
@@ -1151,15 +1153,6 @@ class WidgetAnnotation extends Annotation {
 
     data.readOnly = this.hasFieldFlag(AnnotationFieldFlag.READONLY);
     data.hidden = this._hasFlag(data.annotationFlags, AnnotationFlag.HIDDEN);
-
-    // Hide signatures because we cannot validate them, and unset the fieldValue
-    // since it's (most likely) a `Dict` which is non-serializable and will thus
-    // cause errors when sending annotations to the main-thread (issue 10347).
-    if (data.fieldType === "Sig") {
-      data.fieldValue = null;
-      this.setFlags(AnnotationFlag.HIDDEN);
-      data.hidden = true;
-    }
   }
 
   /**
@@ -1201,7 +1194,7 @@ class WidgetAnnotation extends Annotation {
   getOperatorList(evaluator, task, renderForms, annotationStorage) {
     // Do not render form elements on the canvas when interactive forms are
     // enabled. The display layer is responsible for rendering them instead.
-    if (renderForms) {
+    if (renderForms && !(this instanceof SignatureWidgetAnnotation)) {
       return Promise.resolve(new OperatorList());
     }
 
@@ -1600,13 +1593,6 @@ class WidgetAnnotation extends Annotation {
   }
 
   getFieldObject() {
-    if (this.data.fieldType === "Sig") {
-      return {
-        id: this.data.id,
-        value: null,
-        type: "signature",
-      };
-    }
     return null;
   }
 }
@@ -2203,6 +2189,25 @@ class ChoiceWidgetAnnotation extends WidgetAnnotation {
   }
 }
 
+class SignatureWidgetAnnotation extends WidgetAnnotation {
+  constructor(params) {
+    super(params);
+
+    // Unset the fieldValue since it's (most likely) a `Dict` which is
+    // non-serializable and will thus cause errors when sending annotations
+    // to the main-thread (issue 10347).
+    this.data.fieldValue = null;
+  }
+
+  getFieldObject() {
+    return {
+      id: this.data.id,
+      value: null,
+      type: "signature",
+    };
+  }
+}
+
 class TextAnnotation extends MarkupAnnotation {
   constructor(parameters) {
     const DEFAULT_ICON_SIZE = 22; // px

src/core/document.js

@@ -828,7 +828,12 @@ class PDFDocument {
   }
 
   get formInfo() {
-    const formInfo = { hasFields: false, hasAcroForm: false, hasXfa: false };
+    const formInfo = {
+      hasFields: false,
+      hasAcroForm: false,
+      hasXfa: false,
+      hasSignatures: false,
+    };
     const acroForm = this.catalog.acroForm;
     if (!acroForm) {
       return shadow(this, "formInfo", formInfo);
@@ -854,9 +859,11 @@ class PDFDocument {
       // the first bit of the `SigFlags` integer (see Table 219 in the
       // specification).
       const sigFlags = acroForm.get("SigFlags");
+      const hasSignatures = !!(sigFlags & 0x1);
       const hasOnlyDocumentSignatures =
-        !!(sigFlags & 0x1) && this._hasOnlyDocumentSignatures(fields);
+        hasSignatures && this._hasOnlyDocumentSignatures(fields);
       formInfo.hasAcroForm = hasFields && !hasOnlyDocumentSignatures;
+      formInfo.hasSignatures = hasSignatures;
     } catch (ex) {
       if (ex instanceof MissingDataException) {
         throw ex;
@@ -894,6 +901,7 @@ class PDFDocument {
       IsAcroFormPresent: this.formInfo.hasAcroForm,
       IsXFAPresent: this.formInfo.hasXfa,
       IsCollectionPresent: !!this.catalog.collection,
+      IsSignaturesPresent: this.formInfo.hasSignatures,
     };
 
     let infoDict;

src/shared/util.js

@@ -315,6 +315,7 @@ const UNSUPPORTED_FEATURES = {
   unknown: "unknown",
   forms: "forms",
   javaScript: "javaScript",
+  signatures: "signatures",
   smask: "smask",
   shadingPattern: "shadingPattern",
   /** @deprecated unused */