diff --git a/crates/script/src/prelude.js b/crates/script/src/prelude.js
index 18770041..d6d93f27 100644
--- a/crates/script/src/prelude.js
+++ b/crates/script/src/prelude.js
@@ -179,7 +179,7 @@ File.prototype = {
   get path() { var p = this.__path.split(/[\/\\]/); p.pop(); return p.join("/"); },
   get parent() { return new Folder(this.path); },
   get exists() { return JSON.parse(__file("exists", this.__path)) === true; },
-  get length() { return this.__buf !== null ? this.__buf.length : (this.exists ? JSON.parse(__file("read", this.__path)).length : 0); },
+  get length() { return this.__buf !== null ? this.__buf.length : (this.exists ? JSON.parse(__file(this.encoding.toUpperCase() === "BINARY" ? "readBinary" : "read", this.__path)).length : 0); },
   get eof() { return this.__buf === null || this.__pos >= this.__buf.length; },
   toString: function () { return this.__path; },
   open: function (mode) {
@@ -193,9 +193,9 @@ File.prototype = {
         this.__buf = "";
         return true;
       }
-      this.__buf = JSON.parse(__file("read", this.__path));
+      this.__buf = JSON.parse(__file(this.encoding.toUpperCase() === "BINARY" ? "readBinary" : "read", this.__path));
     } else if (mode === "a") {
-      this.__buf = this.exists ? JSON.parse(__file("read", this.__path)) : "";
+      this.__buf = this.exists ? JSON.parse(__file(this.encoding.toUpperCase() === "BINARY" ? "readBinary" : "read", this.__path)) : "";
       this.__pos = this.__buf.length;
     } else {
       // Check the gate now, like After Effects refusing to open a file for writing.
@@ -232,18 +232,14 @@ File.prototype = {
   tell: function () { return this.__pos; },
   close: function () {
     if ((this.__mode === "w" || this.__mode === "a" || this.__mode === "e") && this.__buf !== null) {
-      __file("write", this.__path, this.__buf);
+      __file(this.encoding.toUpperCase() === "BINARY" ? "writeBinary" : "write", this.__path, this.__buf);
     }
     this.__buf = null;
     this.__mode = null;
     return true;
   },
   remove: function () { return JSON.parse(__file("remove", this.__path)); },
-  copy: function (to) {
-    var data = JSON.parse(__file("read", this.__path));
-    __file("write", __str(to), data);
-    return true;
-  },
+  copy: function (to) { return JSON.parse(__file("copy", this.__path, __str(to))); },
   rename: function () { throw __err("File.rename is not supported"); },
   execute: function () { return JSON.parse(__file("execute", this.__path)); },
   openDlg: function () { return null; },
diff --git a/crates/script/src/runtime.rs b/crates/script/src/runtime.rs
index ffcf90af..225790c4 100644
--- a/crates/script/src/runtime.rs
+++ b/crates/script/src/runtime.rs
@@ -346,8 +346,16 @@ fn check_access(s: &Session, path: &str, write: bool) -> Result<std::path::PathB
     Err(format!("Unable to access {path}: scripts can only read files in the project's folder unless {GATE} is on"))
 }
 
-/// `__file(op, path, data)`: `read` → text, `write`/`append` → bytes, `exists` → bool, `list` →
-/// names, `mkdir`, `remove`, `isDir`.
+/// Encode a binary script string as bytes, without silently corrupting code points outside
+/// the one-byte range supported by ExtendScript's BINARY encoding.
+fn binary_bytes(data: &str) -> Result<Vec<u8>, String> {
+    data.chars()
+        .map(|c| u8::try_from(c as u32).map_err(|_| format!("BINARY encoding cannot represent U+{:04X}", c as u32)))
+        .collect()
+}
+
+/// `__file(op, path, data)`: text and one-byte-per-character BINARY reads/writes,
+/// byte-for-byte copy, plus file and folder operations.
 fn native_file(_: &JsValue, args: &[JsValue], ctx: &mut Context) -> JsResult<JsValue> {
     let op = arg_string(args, 0, ctx)?;
     let path = arg_string(args, 1, ctx)?;
@@ -366,19 +374,36 @@ fn native_file(_: &JsValue, args: &[JsValue], ctx: &mut Context) -> JsResult<JsV
                 let Ok(p) = check_access(s, &path, false) else { return Ok(json!(false)) };
                 Ok(json!(if op == "exists" { p.exists() } else { p.is_dir() }))
             }
-            "read" => {
+            "read" | "readBinary" => {
                 let p = check_access(s, &path, false)?;
                 let bytes = s.services.read_file(&p.to_string_lossy()).map_err(|e| format!("Unable to read {path}: {e}"))?;
-                Ok(json!(String::from_utf8_lossy(&bytes)))
+                if op == "readBinary" {
+                    // Each byte becomes a single JS character (U+0000..U+00FF).
+                    Ok(json!(bytes.into_iter().map(char::from).collect::<String>()))
+                } else {
+                    Ok(json!(String::from_utf8_lossy(&bytes)))
+                }
             }
-            "write" | "append" => {
+            "write" | "writeBinary" | "append" => {
                 let p = check_access(s, &path, true)?;
                 let ps = p.to_string_lossy().to_string();
                 let mut bytes = if op == "append" { s.services.read_file(&ps).unwrap_or_default() } else { vec![] };
-                bytes.extend_from_slice(data.as_bytes());
+                if op == "writeBinary" {
+                    bytes.extend(binary_bytes(&data)?);
+                } else {
+                    bytes.extend_from_slice(data.as_bytes());
+                }
                 s.services.write_file(&ps, &bytes).map_err(|e| format!("Unable to write {path}: {e}"))?;
                 Ok(json!(bytes.len()))
             }
+            "copy" => {
+                let src = check_access(s, &path, false)?;
+                let dst = check_access(s, &data, true)?;
+                // Copy the original bytes, not UTF-8-decoded script text.
+                let bytes = s.services.read_file(&src.to_string_lossy()).map_err(|e| format!("Unable to read {path}: {e}"))?;
+                s.services.write_file(&dst.to_string_lossy(), &bytes).map_err(|e| format!("Unable to write {data}: {e}"))?;
+                Ok(json!(true))
+            }
             "list" => {
                 let p = check_access(s, &path, false)?;
                 let mut names: Vec<String> = std::fs::read_dir(&p)
diff --git a/crates/script/src/tests.rs b/crates/script/src/tests.rs
index b50a7bfb..dd08f2eb 100644
--- a/crates/script/src/tests.rs
+++ b/crates/script/src/tests.rs
@@ -730,3 +730,49 @@ fn import_options_sequence_picks_one_still_or_the_run() {
     assert_eq!(kind_of(&s, "shot_[0001-0003].png"), FootageKind::Sequence);
     let _ = std::fs::remove_dir_all(&dir);
 }
+
+
+#[test]
+fn binary_file_io_preserves_all_byte_values() {
+    let dir = std::env::temp_dir().join(format!("ec-script-binary-{}", std::process::id()));
+    std::fs::create_dir_all(&dir).unwrap();
+    let src = dir.join("sig.bin");
+    let dst = dir.join("written.bin");
+    let copied = dir.join("copied.bin");
+    let original = [0x89u8, 0x50, 0x4e, 0x47, 0x00, 0x7f, 0x80, 0xff, 0x0a];
+    std::fs::write(&src, original).unwrap();
+    let mut s = session();
+    s.path = Some(dir.join("project.ecproj").to_string_lossy().to_string());
+    s.prefs.scripting.allow_scripts_write_files = true;
+    let q = |p: &std::path::Path| serde_json::to_string(&p.to_string_lossy()).unwrap();
+
+    let read = ok(&mut s, &format!(
+        "var f = new File({}); f.encoding = 'BINARY'; f.open('r'); var data = f.read(); f.close(); [data.length, data.charCodeAt(0), data.charCodeAt(6), data.charCodeAt(7)]",
+        q(&src)
+    ));
+    assert_eq!(read.result, json!([9, 0x89, 0x80, 0xff]));
+
+    ok(&mut s, &format!(
+        "var f = new File({}); f.encoding = 'BINARY'; f.open('w'); f.write(String.fromCharCode(0x89, 0x50, 0x4e, 0x47, 0, 127, 128, 255, 10)); f.close();",
+        q(&dst)
+    ));
+    assert_eq!(std::fs::read(&dst).unwrap(), original);
+
+    let copy = ok(&mut s, &format!("new File({}).copy({})", q(&src), q(&copied)));
+    assert_eq!(copy.result, json!(true));
+    assert_eq!(std::fs::read(&copied).unwrap(), original);
+
+    ok(&mut s, &format!(
+        "var f = new File({}); f.encoding = 'BINARY'; f.open('a'); f.write(String.fromCharCode(0xfe)); f.close();",
+        q(&dst)
+    ));
+    assert_eq!(std::fs::read(&dst).unwrap(), [original.as_slice(), &[0xfe]].concat());
+
+    let invalid = run_code(
+        &mut s,
+        &format!("var f = new File({}); f.encoding = 'BINARY'; f.open('w'); f.write(String.fromCharCode(0x100)); f.close();", q(&dst)),
+        "invalid-binary.jsx",
+    );
+    assert!(invalid.error.is_some(), "code points above 255 must not be truncated");
+    let _ = std::fs::remove_dir_all(&dir);
+}