diff --git a/src/core/obj.js b/src/core/obj.js
index f4b9d2e85..0e1ffbcb6 100644
--- a/src/core/obj.js
+++ b/src/core/obj.js
@@ -355,6 +355,67 @@ class Catalog {
       return onParsed;
     }
 
+    function parseOrder(refs, nestedLevels = 0) {
+      if (!Array.isArray(refs)) {
+        return null;
+      }
+      const order = [];
+
+      for (const value of refs) {
+        if (isRef(value) && contentGroupRefs.includes(value)) {
+          parsedOrderRefs.put(value); // Handle "hidden" groups, see below.
+
+          order.push(value.toString());
+          continue;
+        }
+        // Handle nested /Order arrays (see e.g. issue 9462 and bug 1240641).
+        const nestedOrder = parseNestedOrder(value, nestedLevels);
+        if (nestedOrder) {
+          order.push(nestedOrder);
+        }
+      }
+
+      if (nestedLevels > 0) {
+        return order;
+      }
+      const hiddenGroups = [];
+      for (const groupRef of contentGroupRefs) {
+        if (parsedOrderRefs.has(groupRef)) {
+          continue;
+        }
+        hiddenGroups.push(groupRef.toString());
+      }
+      if (hiddenGroups.length) {
+        order.push({ name: null, order: hiddenGroups });
+      }
+
+      return order;
+    }
+
+    function parseNestedOrder(ref, nestedLevels) {
+      if (++nestedLevels > MAX_NESTED_LEVELS) {
+        warn("parseNestedOrder - reached MAX_NESTED_LEVELS.");
+        return null;
+      }
+      const value = xref.fetchIfRef(ref);
+      if (!Array.isArray(value)) {
+        return null;
+      }
+      const nestedName = xref.fetchIfRef(value[0]);
+      if (typeof nestedName !== "string") {
+        return null;
+      }
+      const nestedOrder = parseOrder(value.slice(1), nestedLevels);
+      if (!nestedOrder || !nestedOrder.length) {
+        return null;
+      }
+      return { name: stringToPDFString(nestedName), order: nestedOrder };
+    }
+
+    const xref = this.xref,
+      parsedOrderRefs = new RefSet(),
+      MAX_NESTED_LEVELS = 10;
+
     return {
       name: isString(config.get("Name"))
         ? stringToPDFString(config.get("Name"))
@@ -367,6 +428,8 @@ class Catalog {
         : null,
       on: parseOnOff(config.get("ON")),
       off: parseOnOff(config.get("OFF")),
+      order: parseOrder(config.get("Order")),
+      groups: null,
     };
   }
 
diff --git a/src/display/api.js b/src/display/api.js
index f9a295dcc..bb7b184a6 100644
--- a/src/display/api.js
+++ b/src/display/api.js
@@ -778,9 +778,9 @@ class PDFDocumentProxy {
   }
 
   /**
-   * @returns {Promise<OptionalContentConfig | null>} A promise that is resolved
-   *   with an {@link OptionalContentConfig} that has all the optional content
-   *   groups, or `null` if the document does not have any.
+   * @returns {Promise<OptionalContentConfig>} A promise that is resolved with
+   *   an {@link OptionalContentConfig} that contains all the optional content
+   *   groups (assuming that the document has any).
    */
   getOptionalContentConfig() {
     return this._transport.getOptionalContentConfig();
diff --git a/src/display/optional_content_config.js b/src/display/optional_content_config.js
index 16308623d..5e14c1284 100644
--- a/src/display/optional_content_config.js
+++ b/src/display/optional_content_config.js
@@ -26,6 +26,7 @@ class OptionalContentConfig {
   constructor(data) {
     this.name = null;
     this.creator = null;
+    this._order = null;
     this.groups = new Map();
 
     if (data === null) {
@@ -33,6 +34,7 @@ class OptionalContentConfig {
     }
     this.name = data.name;
     this.creator = data.creator;
+    this._order = data.order;
     for (const group of data.groups) {
       this.groups.set(
         group.id,