diff --git a/crates/engine/src/tests_envelope.rs b/crates/engine/src/tests_envelope.rs
index 78006942..f1609d89 100644
--- a/crates/engine/src/tests_envelope.rs
+++ b/crates/engine/src/tests_envelope.rs
@@ -52,6 +52,14 @@ fn options(s: &Session, id: NodeId) -> (EnvelopeOptions, f64) {
     }
 }
 
+/// `bytes` without the lines that depend on when the file was written: the EPS and PDF dates, and
+/// a PDF's XMP packet (one line, with its dates and IDs) and trailer `/ID`.
+fn undated(bytes: &[u8]) -> Vec<u8> {
+    let stamps: [&[u8]; 5] = [b"CreationDate", b"ModDate", b"xmp:CreateDate", b"xmp:ModifyDate", b"/ID["];
+    let dated = |line: &&[u8]| stamps.iter().any(|s| line.windows(s.len()).any(|w| w == *s));
+    bytes.split(|b| *b == b'\n').filter(|l| !dated(l)).flat_map(|l| l.iter().copied().chain(*b"\n")).collect()
+}
+
 #[test]
 fn new_envelopes_take_the_reference_defaults_and_options_change_them() {
     let mut s = session();
@@ -221,13 +229,19 @@ fn enveloped_type_exports_distorted_in_every_format() {
     let t = id_of(&s.execute("text.create", &json!({"x": 100, "y": 200, "text": "Envelope", "size": 48})).unwrap());
     sel(&mut s, &[t]);
     s.execute("object.envelope.makeWithWarp", &json!({"style": "arch", "bend": 0})).unwrap();
-    // The export's bytes without its time stamps (EPS and PDF date their files to the second).
+    // The export's bytes without its dates and file ID (EPS and PDF date their files to the second).
     let export = |s: &mut Session, format: &str| -> Vec<u8> {
         let data = s.execute("document.export", &json!({"format": format})).unwrap()["dataBase64"].as_str().unwrap().to_string();
-        let bytes = vectorcraft_format::base64_decode(&data).unwrap();
-        let dated = |line: &&[u8]| line.windows(12).any(|w| w == b"CreationDate") || line.windows(7).any(|w| w == b"ModDate");
-        bytes.split(|b| *b == b'\n').filter(|l| !dated(l)).flat_map(|l| l.iter().copied().chain(*b"\n")).collect()
+        undated(&vectorcraft_format::base64_decode(&data).unwrap())
     };
+    // Two PDFs dated a second apart, with the options and editing data that document.export
+    // passes the writer, differ only in lines that `undated` drops.
+    let d = &s.doc().unwrap().doc;
+    let pdf = |at: i64| {
+        let o = cmd::fileio::pdf::options("document.export", d, &json!({})).unwrap();
+        undated(&export_pdf(d, &vectorcraft_pdf::PdfOptions { created: Some(at), native: Some(vectorcraft_format::save(d, false)), ..o }).unwrap())
+    };
+    assert_eq!(pdf(0), pdf(1), "a PDF dated a second later differs only in its dates and file ID");
     for format in ["svg", "pdf", "eps", "emf", "dxf"] {
         s.execute("object.envelope.options", &json!({"bend": 0})).unwrap();
         let flat = export(&mut s, format);