<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>File Upload Form</title>
</head>
<body>
<h2>Upload File</h2>
<form action="/upload" method="post" enctype="multipart/form-data">
<label for="file">Select a file:</label>
<input type="file" id="file" name="file" accept=".txt, .pdf, .doc, .docx">
<br><br>
<button type="submit">Upload</button>
</form>
</body>
</html>注意：当一个表单包含<input type="file">时，表单的enctype必须指定为multipart/form-data，method必须指定为post，浏览器才能正确编码并以multipart/form-data格式发送表单的数据。