diff --git a/public/pdfjs/web/viewer.html b/public/pdfjs/web/viewer.html
index 41f181de..6d3236c2 100644
--- a/public/pdfjs/web/viewer.html
+++ b/public/pdfjs/web/viewer.html
@@ -38,7 +38,7 @@ See https://github.com/adobe-type-tools/cmap-resources
 </head>
 
 <body tabindex="1">
-<div id="outerContainer" style="user-select: none">
+<div id="outerContainer">
 
   <div id="sidebarContainer">
     <div id="toolbarSidebar">
@@ -581,4 +581,17 @@ See https://github.com/adobe-type-tools/cmap-resources
 
 <input type="file" id="fileInput" class="hidden">
 </body>
+
+<script>
+  const previewDom = document.getElementById('viewerContainer')
+  const handleSelectionChange = (event) => {
+    const windowSelection = window.getSelection()
+    const selectionText = windowSelection ? window.getSelection().toString() : document.selection.createRange().text
+    if (selectionText.length > 500) {
+      alert('超出可复制长度')
+      windowSelection ? window.getSelection().removeAllRanges() : document.selection.empty()
+    }
+  }
+  document.addEventListener('selectionchange', handleSelectionChange)
+</script>
 </html>
