在浏览器中不使用PDF中的“标题”查看PDF内容

Question

我必须用PHP查看pdf的内容。 尝试了很多我在互联网上找到的示例，但没有查看pdf的内容

我尝试使用此代码：

<?php
$filePath="pdffiles/";
$filename="2018-06-0343.pdf";
header('Content-type:application/pdf');
header('Content-disposition: inline; filename="'.$filename.'"');
header('content-Transfer-Encoding:binary');
header('Accept-Ranges:bytes');
@ readfile($filePath)
?>

我收到此错误，因为它在子文件中

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\sample\main.php:77) in C:\xampp\htdocs\sample\pages\subfile.php on line 25

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\sample\main.php:77) in C:\xampp\htdocs\sample\pages\subfile.php on line 26

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\sample\main.php:77) in C:\xampp\htdocs\sample\pages\subfile.php on line 27

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\sample\main.php:77) in C:\xampp\htdocs\sample\pages\subfile.php on line 28

是否有不使用标题即可查看PDF内容的最佳方法？