diff --git a/crates/engine/src/js.rs b/crates/engine/src/js.rs
index c80537fba..a59743dbb 100644
--- a/crates/engine/src/js.rs
+++ b/crates/engine/src/js.rs
@@ -129,8 +129,16 @@ pub struct JsRunner {
 }
 
 impl JsRunner {
+    /// A runner for `cos`: what scripts read about the document (pages, info, whether it is
+    /// an XFA form) and its document-level scripts, read once.
     pub fn new(cos: &pdfcraft_cos::Document, file_name: &str) -> JsRunner {
-        let doc = pdfcraft_js::DocInfo { file_name: file_name.to_string(), num_pages: pdfcraft_model::pages(cos).len(), page: 0, info: info(cos) };
+        let doc = pdfcraft_js::DocInfo {
+            file_name: file_name.to_string(),
+            num_pages: pdfcraft_model::pages(cos).len(),
+            page: 0,
+            info: info(cos),
+            xfa: pdfcraft_xfa::xfa_shape(cos).is_some(),
+        };
         JsRunner {
             doc,
             doc_scripts: pdfcraft_forms::document_scripts(cos),
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index afe6fd06c..c8f0eb886 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -4076,6 +4076,20 @@ fn form_javascript_validates_calculates_and_formats() {
     assert!(s.run_javascript(id, "1", None).is_err());
 }
 
+/// XFA forms check `xfa_installed` and `xfa_version` in a document script that runs before
+/// each of their scripts, and alert when either is missing.
+#[test]
+fn scripts_in_an_xfa_form_see_the_xfa_plugin_installed() {
+    let check = "typeof xfa_installed + ' ' + typeof xfa_version + ' ' + xfa_version";
+    let mut s = Session::new().with_clock(|| 1_700_000_000);
+    let xfa = s.open("form.pdf", None, Arc::new(pdfcraft_xfa::fixtures::shell(&pdfcraft_xfa::fixtures::template(3))), None).unwrap();
+    let o = s.run_javascript(xfa, check, None).unwrap();
+    assert_eq!((o.error, o.result.as_deref()), (None, Some("boolean number 3.5")));
+    let plain = s.open("order.pdf", None, Arc::new(scripted_form()), None).unwrap();
+    let o = s.run_javascript(plain, check, None).unwrap();
+    assert_eq!((o.error, o.result.as_deref()), (None, Some("undefined number 3.5")));
+}
+
 #[test]
 fn edit_history_does_not_replay_field_script_side_effects() {
     let mut s = Session::new().with_clock(|| 1_700_000_000);
diff --git a/crates/js/src/lib.rs b/crates/js/src/lib.rs
index f2221f750..13bdc4ba3 100644
--- a/crates/js/src/lib.rs
+++ b/crates/js/src/lib.rs
@@ -144,6 +144,8 @@ pub struct DocInfo {
     pub page: usize,
     /// Document information (`this.info.title` etc.): lower-case key, value.
     pub info: Vec<(String, String)>,
+    /// The document has an XFA form, so scripts see `xfa_installed`.
+    pub xfa: bool,
 }
 
 /// Something a script asked the viewer to do.
@@ -971,6 +973,11 @@ fn color_object(ctx: &mut Context) -> JsObject {
     o.build()
 }
 
+/// The XFA version scripts see as `xfa_version`.
+const XFA_VERSION: f64 = 3.5;
+
+/// Define the globals every script sees: the document's functions and properties (`getField`,
+/// `numPages`, `info`, the XFA version), and `app`, `util`, `console`, `display` and `color`.
 fn install(ctx: &mut Context) -> JsResult<()> {
     let globals: [(&str, usize, NativeFunction); 9] = [
         ("getField", 1, NativeFunction::from_fn_ptr(get_field)),
@@ -991,9 +998,9 @@ fn install(ctx: &mut Context) -> JsResult<()> {
     let nf = function(ctx, NativeFunction::from_fn_ptr(num_fields));
     let pg = function(ctx, NativeFunction::from_fn_ptr(page_num_get));
     let ps = function(ctx, NativeFunction::from_fn_ptr(page_num_set));
-    let (file, pages, info) = {
+    let (file, pages, info, xfa) = {
         let h = host(ctx)?.borrow();
-        (h.doc.file_name.clone(), h.doc.num_pages, h.doc.info.clone())
+        (h.doc.file_name.clone(), h.doc.num_pages, h.doc.info.clone(), h.doc.xfa)
     };
     let mut io = ObjectInitializer::new(ctx);
     for (k, v) in &info {
@@ -1006,6 +1013,12 @@ fn install(ctx: &mut Context) -> JsResult<()> {
     ctx.register_global_property(js_string!("numPages"), JsValue::from(pages as f64), rw)?;
     ctx.register_global_property(js_string!("documentFileName"), s(&file), rw)?;
     ctx.register_global_property(js_string!("info"), info, rw)?;
+    // XFA forms check both before they run: every document sees the XFA version, and only an
+    // XFA form sees `xfa_installed`.
+    ctx.register_global_property(js_string!("xfa_version"), JsValue::from(XFA_VERSION), rw)?;
+    if xfa {
+        ctx.register_global_property(js_string!("xfa_installed"), JsValue::from(true), rw)?;
+    }
 
     let app = ObjectInitializer::new(ctx)
         .function(NativeFunction::from_fn_ptr(alert), js_string!("alert"), 1)
diff --git a/crates/js/src/tests.rs b/crates/js/src/tests.rs
index 7d63b4998..b2e866fae 100644
--- a/crates/js/src/tests.rs
+++ b/crates/js/src/tests.rs
@@ -16,7 +16,7 @@ fn fields() -> Vec<FieldState> {
 }
 
 fn doc() -> DocInfo {
-    DocInfo { file_name: "order.pdf".into(), num_pages: 3, page: 0, info: vec![("title".into(), "Order".into())] }
+    DocInfo { file_name: "order.pdf".into(), num_pages: 3, page: 0, info: vec![("title".into(), "Order".into())], xfa: false }
 }
 
 fn go(script: &str, event: &Event) -> Outcome {
@@ -1454,3 +1454,29 @@ fn shared_field_snapshots_isolate_writes_errors_and_script_globals() {
     assert_eq!(read.value, "undefined:4:false");
     assert!(read.changed.is_empty());
 }
+
+/// The check XFA forms run on opening: without both globals, or with a version below 2.8, it
+/// alerts that the viewer can't show the form.
+const XFA_CHECK: &str = "if (typeof(xfa_installed) == 'undefined' || typeof(xfa_version) == 'undefined' || xfa_version < 2.8) app.alert('old viewer'); \
+                         event.value = typeof xfa_installed + ' ' + typeof xfa_version + ' ' + xfa_version;";
+
+/// An XFA form sees `xfa_installed` (true) and `xfa_version` (3.5), so the check passes.
+#[test]
+fn an_xfa_form_sees_the_xfa_plugin_installed() {
+    let xfa = DocInfo { xfa: true, ..doc() };
+    let o = run(XFA_CHECK, &Event::doc("Open"), &xfa, &fields(), &[], Limits::default());
+    assert_eq!(o.error, None);
+    assert_eq!(o.value, "boolean number 3.5");
+    assert!(o.alerts.is_empty(), "{:?}", o.alerts);
+    let o = run("event.value = String(xfa_installed);", &Event::doc("Open"), &xfa, &fields(), &[], Limits::default());
+    assert_eq!(o.value, "true");
+}
+
+/// A form without XFA sees `xfa_version` but no `xfa_installed`, so the check alerts.
+#[test]
+fn a_plain_form_sees_the_xfa_version_but_not_installed() {
+    let o = go(XFA_CHECK, &Event::doc("Open"));
+    assert_eq!(o.error, None);
+    assert_eq!(o.value, "undefined number 3.5");
+    assert_eq!(o.alerts, ["old viewer"]);
+}
diff --git a/parity/acrobat-features.toml b/parity/acrobat-features.toml
index 6200bac36..973e0cc69 100644
--- a/parity/acrobat-features.toml
+++ b/parity/acrobat-features.toml
@@ -5165,8 +5165,8 @@ milestone = "M6"
 status = "partial"
 commands = ["tools.js_console"]
 tools = ["js_run"]
-evidence = ["crates/js/src/tests.rs::calculate_scripts_read_fields_and_set_the_value", "crates/engine/src/tests.rs::form_javascript_validates_calculates_and_formats", "crates/automation/tests/it/automation.rs::javascript_through_tools"]
-notes = "boa (pure Rust) with the forms object model: event, getField/Field (value, readonly, display, colours, items, check boxes), app, util.printf/printd/printx, console, display, color; no annotations, layers or dialogs (app.response returns null) yet."
+evidence = ["crates/js/src/tests.rs::calculate_scripts_read_fields_and_set_the_value", "crates/engine/src/tests.rs::form_javascript_validates_calculates_and_formats", "crates/automation/tests/it/automation.rs::javascript_through_tools", "crates/js/src/tests.rs::an_xfa_form_sees_the_xfa_plugin_installed", "crates/js/src/tests.rs::a_plain_form_sees_the_xfa_version_but_not_installed", "crates/engine/src/tests.rs::scripts_in_an_xfa_form_see_the_xfa_plugin_installed"]
+notes = "boa (pure Rust) with the forms object model: event, getField/Field (value, readonly, display, colours, items, check boxes), app, util.printf/printd/printx, console, display, color; xfa_version (3.5) in every document and xfa_installed in XFA forms, so their version check passes; no annotations, layers or dialogs (app.response returns null) yet, and no app.findComponent."
 
 [[feature]]
 id = "form.js-console"