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Asked: 2024-12-21T11:14:19+05:30

How can I determine the number of pages in a digitally signed PDF document using PHP or JavaScript?

I’ve been stuck on a little project, and I could really use some input from anyone who’s dabbled in this area. So here’s the deal: I have a digitally signed PDF document, and I need to figure out how to count the number of pages in it using either PHP or JavaScript.

You know how sometimes you’re working with PDFs and all the features can get a bit tangled? I’ve got this PDF that’s signed, and while it’s great for security, it seems like it complicates things a bit when trying to extract information from it. I want to pull the page count so I can display some stats or something about the document, but I’m not sure of the best way to approach this.

I’ve tried a couple of popular libraries already. For PHP, I looked into using FPDF and TCPDF, but I found out those don’t really handle signed PDFs well. Then there’s also PDFtk, but the command line stuff gets a little messy. I’ve even considered using Poppler, but there’s a lot of setup required, and I’m not sure if it’s overkill for just counting pages.

On the JavaScript side, I’m exploring options like PDF.js, but I’ve stumbled upon a couple of issues with loaded documents that are digitally signed. It seems that when I try to extract the number of pages, it sometimes fails or returns incorrect values. Has anyone had any luck with this?

If you’ve worked on something similar or know of a reliable library that can help with this, I’d love to hear about it. It would be awesome to save time and frustration here, as I’m trying to develop a feature that will make my users’ lives easier.

So, do you guys have any tips, tricks, or experience you could share? Any help would be super appreciated! Thanks in advance!

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    2 Answers

    1. Counting pages in a digitally signed PDF can definitely be tricky, especially if you’ve run into issues with some of the libraries! Since you’re using PHP and JavaScript, I’ll share some pointers based on what I’ve heard.

      For PHP, you might want to give pdfinfo from the Poppler utility a shot. This tool is often recommended because it can handle signed PDFs better than FPDF or TCPDF. You can run it from the command line and parse the output in your PHP script. It’s like:

      exec('pdfinfo yourfile.pdf', $output);

      This might give you the page count without all the extra setup hassle.

      On the JavaScript side, PDF.js is pretty popular, but I totally get the challenges with digital signatures. If you’ve got the PDF loaded using PDF.js, you should be able to access the number of pages with something like:

      PDFJS.getDocument('yourfile.pdf').promise.then(function(pdf) {
        console.log('Number of pages:', pdf.numPages);
    });

      Sometimes, issues with signed PDFs can arise if the signature validation fails or if the PDF is slightly malformed. If you’re still running into problems, consider checking if the PDF loads without validation, or use an alternative like pdf-lib. It’s another library that might handle signed PDFs better.

      A lot of it depends on how strictly the PDF conforms to standards, so experimenting with a few different libraries might be worthwhile! Keep at it, and I hope you find something that clicks!

    2. When working with digitally signed PDF documents, extracting information like the page count can indeed present unique challenges, especially when using popular PHP libraries. Since FPDF and TCPDF typically struggle with signed PDFs, you might want to consider using the PDFBox library, which is quite effective for handling PDF files, including those that are signed. PDFBox allows you to interactively parse the document and retrieve the number of pages without getting bogged down in complicated command-line setups. Additionally, if you must utilize command-line tools, the pdfinfo utility from the Poppler package seldom faces issues with signed PDFs. It provides straightforward output of page counts and other metadata, which may simplify your project significantly.

      On the JavaScript front, PDF.js is a great library for rendering PDFs directly in the browser. However, dealing with signed PDFs indeed leads to some limitations. One potential workaround is to ensure that your PDFs are not altered post-signing, as any modification may lead PDF.js to misinterpret the document structure. A helpful tip could be to load the PDF into a blob URL and then use PDF.js’s getPageCount functionality to determine the number of pages. If you’re still encountering issues with page counts, consider checking the integrity of the digital signature and ensuring that the document is opened in a stable environment. Otherwise, combining PDF.js with some server-side processing using Node.js could bridge the gap in handling complexities around signed documents.