Hey there! Let's break down your three questions about KnpSnappyBundle and fix the issues you're running into with your controller code.

Feature Support Breakdown #

First, let's confirm what's possible:

• Merge multiple PDFs: Yes, it's supported, but relies on proper handling of input files (local files are far more reliable than remote URLs).
• Convert images to PDF: Absolutely supported, but you need to ensure images are loaded correctly and configure wkhtmltopdf properly.
• Load local PDF files: Yes, this is the most stable way to work with PDFs in KnpSnappy—just use the local file path instead of a URL.

Fixing Your Controller Issues #

1. PDF Merging Error #

Your error comes from wkhtmltopdf struggling to load remote PDF files (it's designed primarily for HTML, not remote PDF fetching) plus extra spaces around your URLs in the generated command. Here's the exact error you hit:

The exit status code '1' says something went wrong:
stderr: "Loading pages (1/6)
[> ] 0%
[=> ] 5%
[====> ] 10%
Error: Failed loading page http://www.pdf995.com/samples/pdf.pdf (sometimes it will work just to ignore this error with --load-error-handling ignore)
Error: Failed loading page http://www.africau.edu/images/default/sample.pdf (sometimes it will work just to ignore this error with --load-error-handling ignore)
Exit with code 1, due to unknown error. "
stdout: ""
command: /usr/bin/wkhtmltopdf --lowquality ' http://www.pdf995.com/samples/pdf.pdf ' ' http://www.africau.edu/images/default/sample.pdf ' 'merge.pdf'.

Fix Option 1: Use Local PDF Files

Download the PDFs to your project first, then use their local paths:

public function pdfAction()
{
    // Path to your project's public directory
    $publicDir = $this->kernel->getProjectDir() . '/public';
    
    // Assume you've saved the PDFs here
    $localPdf1 = $publicDir . '/sample1.pdf';
    $localPdf2 = $publicDir . '/sample2.pdf';

    // Merge local PDFs
    $this->pdf->generate([$localPdf1, $localPdf2], $publicDir . '/merged.pdf');
}

Fix Option 2: Download Remote PDFs to Temp Files First

If you need to pull remote PDFs dynamically, download them to temporary files before merging:

use Symfony\Component\HttpFoundation\File\TempFile;

public function pdfAction()
{
    $publicDir = $this->kernel->getProjectDir() . '/public';
    
    // Create temp files for remote PDFs
    $tempPdf1 = new TempFile();
    file_put_contents($tempPdf1->getPathname(), file_get_contents('http://www.pdf995.com/samples/pdf.pdf'));
    
    $tempPdf2 = new TempFile();
    file_put_contents($tempPdf2->getPathname(), file_get_contents('http://www.africau.edu/images/default/sample.pdf'));

    // Merge temp files
    $this->pdf->generate([$tempPdf1->getPathname(), $tempPdf2->getPathname()], $publicDir . '/merged.pdf');
}

2. Empty PDF from Image Conversion #

Your empty PDF is caused by wkhtmltopdf failing to load the remote image (or not rendering it properly). Fix this by using a local image and adding critical rendering options:

public function pdfAction()
{
    $publicDir = $this->kernel->getProjectDir() . '/public';
    $localImage = $publicDir . '/minion.jpg';

    // Download the image locally first
    file_put_contents($localImage, file_get_contents('https://www.cleverfiles.com/howto/wp-content/uploads/2018/03/minion.jpg'));

    // Add options to ensure proper image rendering
    $this->pdf->setOption('enable-javascript', true);
    $this->pdf->setOption('load-error-handling', 'ignore');

    // Convert local image to PDF
    $this->pdf->generate($localImage, $publicDir . '/jpgToPdf.pdf');
}

3. Loading Local PDF Files #

As shown above, simply pass the absolute local file path to generate():

public function pdfAction()
{
    $localPdf = $this->kernel->getProjectDir() . '/public/my-local-file.pdf';
    $outputPath = $this->kernel->getProjectDir() . '/public/output.pdf';

    // Use the local PDF as input (for merging, conversion, etc.)
    $this->pdf->generate($localPdf, $outputPath);
}

Key Tips #

• KnpSnappy is just a wrapper for wkhtmltopdf—experiment with its command-line parameters via setOption() to tweak behavior.
• Remote resources (PDFs/images) are prone to network issues, access limits, or loading errors—always prefer local files for stability.
• If you hit loading errors, use the --load-error-handling ignore option to skip non-fatal issues, as suggested in your error message.

内容的提问来源于stack exchange，提问作者AiD