Open PDF file on Front End of WordPress

I have a custom plugin that works great. I added an ability to save a generated PDF file on the server, within a seperate plugin based folder. The folder has read and execute permissions.

On the backend it reads and displays fine. ON the front is says:

Error Failed to load PDF document.

Anyone have any thoughts as to why? The file is already created and stored. This is just a read and display.

The code is as follows:

$PluginDir     = plugin_dir_path( __DIR__ );
$ServerVault   = $PluginDir . 'plugin-name/ServerVault/';
$filename      = 'file.pdf';
$SavedResults  = $ServerVault . $filename;

header("Content-type: application/pdf");
header("Content-Length: " . filesize($SavedResults));
   
@readfile($SavedResults);

Solution

Based on the information you provided there should be some things you should check.

First of all, don't suppress errors with @readfile().
If you have an error there, please update your post so we can see what is the error exactly.
**
However:

1. Check if file really exists and is readable:

if (!file_exists($SavedResults)) {
    http_response_code(404);
    exit("File not found.");
}

if (!is_readable($SavedResults)) {
    http_response_code(403);
    exit("File not readable.");
}

2. Try adding Content-Disposition header:

header("Content-type: application/pdf");
header("Content-Disposition: inline; filename=\"$filename\"");
header("Content-Length: " . filesize($SavedResults));
readfile($SavedResults);
exit;

3. Sometimes wordpress adds output buffering, clear it before putting PDF to output:

while (ob_get_level()) {
    ob_end_clean();
}

header("Content-type: application/pdf");
header("Content-Disposition: inline; filename=\"$filename\"");
header("Content-Length: " . filesize($SavedResults));
readfile($SavedResults);
exit;

Additionally, I would say validate the plugin_dir_path(_DIR_) that is resolves the correct directory.

Let me know if any of this helps!