diff --git a/src/scripting_api/event.js b/src/scripting_api/event.js
index f4036bb26..b0f3c26f7 100644
--- a/src/scripting_api/event.js
+++ b/src/scripting_api/event.js
@@ -76,6 +76,11 @@ class EventDispatcher {
         event.name = baseEvent.name;
       }
       if (id === "doc") {
+        if (event.name === "Open") {
+          // Before running the Open event, we format all the fields
+          // (see bug 1766987).
+          this.formatAll();
+        }
         this._document.obj._dispatchDocEvent(event.name);
       } else if (id === "page") {
         this._document.obj._dispatchPageEvent(
@@ -180,6 +185,20 @@ class EventDispatcher {
     }
   }
 
+  formatAll() {
+    // Run format actions if any for all the fields.
+    const event = (globalThis.event = new Event({}));
+    for (const source of Object.values(this._objects)) {
+      event.value = source.obj.value;
+      if (this.runActions(source, source, event, "Format")) {
+        source.obj._send({
+          id: source.obj._id,
+          formattedValue: event.value?.toString?.(),
+        });
+      }
+    }
+  }
+
   runValidation(source, event) {
     const didValidateRun = this.runActions(source, source, event, "Validate");
     if (event.rc) {
diff --git a/test/integration/scripting_spec.js b/test/integration/scripting_spec.js
index d7f7f65b2..e50f371dd 100644
--- a/test/integration/scripting_spec.js
+++ b/test/integration/scripting_spec.js
@@ -1302,4 +1302,38 @@ describe("Interaction", () => {
       );
     });
   });
+
+  describe("in bug1766987.pdf", () => {
+    let pages;
+
+    beforeAll(async () => {
+      pages = await loadAndWait("bug1766987.pdf", "#\\37 5R");
+    });
+
+    afterAll(async () => {
+      await closePages(pages);
+    });
+
+    it("must check that field value is correctly formatted", async () => {
+      await Promise.all(
+        pages.map(async ([browserName, page]) => {
+          await page.waitForFunction(
+            "window.PDFViewerApplication.scriptingReady === true"
+          );
+
+          let text = await page.$eval("#\\37 5R", el => el.value);
+          expect(text).withContext(`In ${browserName}`).toEqual("150.32 €");
+
+          text = await page.$eval("#\\38 2R", el => el.value);
+          expect(text).withContext(`In ${browserName}`).toEqual("12.74 Kwh");
+
+          text = await page.$eval("#\\39 1R", el => el.value);
+          expect(text).withContext(`In ${browserName}`).toEqual("352.19 Kwh");
+
+          text = await page.$eval("#\\31 01R", el => el.value);
+          expect(text).withContext(`In ${browserName}`).toEqual("20.57 €");
+        })
+      );
+    });
+  });
 });
diff --git a/test/pdfs/bug1766987.pdf.link b/test/pdfs/bug1766987.pdf.link
new file mode 100644
index 000000000..77ac63228
--- /dev/null
+++ b/test/pdfs/bug1766987.pdf.link
@@ -0,0 +1,2 @@
+https://bugzilla.mozilla.org/attachment.cgi?id=9274388
+
diff --git a/test/test_manifest.json b/test/test_manifest.json
index 0bca13fe1..b46951ab9 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -6494,5 +6494,12 @@
           "value": "05/17/2022"
         }
       }
+   },
+   { "id": "bug1766987",
+      "file": "pdfs/bug1766987.pdf",
+      "md5": "3ce134ead03d6158c3e8207453dcd21d",
+      "rounds": 1,
+      "link": true,
+      "type": "other"
    }
 ]