diff --git a/crates/zx_document_core/src/material_type.rs b/crates/zx_document_core/src/material_type.rs
index 926ff15..bb0eb85 100644
--- a/crates/zx_document_core/src/material_type.rs
+++ b/crates/zx_document_core/src/material_type.rs
@@ -4,7 +4,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::error::DocumentError;
 
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, uniffi::Enum)]
 pub enum MaterialType {
     Markdown,
     Text,
@@ -17,7 +17,7 @@ pub enum MaterialType {
     Unknown,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, uniffi::Enum)]
 pub enum PreviewMode {
     NativeReader,
     PlatformPreview,
@@ -47,8 +47,15 @@ impl MaterialType {
 pub fn detect_material_type(file_path: &str) -> Result<MaterialType, DocumentError> {
     let path = Path::new(file_path);
 
-    // 1. Read file header for magic bytes detection
-    if let Ok(buf) = std::fs::read(file_path) {
+    // 1. Read file header (first 8KB) for magic bytes detection
+    let header = std::fs::File::open(file_path).ok().and_then(|mut f| {
+        use std::io::Read;
+        let mut buf = vec![0u8; 8192];
+        let n = f.read(&mut buf).unwrap_or(0);
+        buf.truncate(n);
+        Some(buf)
+    });
+    if let Some(buf) = header {
         if let Some(info) = infer::get(&buf) {
             let inferred = match info.mime_type() {
                 "application/pdf" => Some(MaterialType::Pdf),