Document conversion PDF to image and DOCX to PDF on server

Implementing Document Conversion (PDF → Image, DOCX → PDF) on Server

Two most common server conversion scenarios: convert PDF pages to images (for previews, thumbnails) and convert DOCX to PDF (for unified format downloads, printing, archiving).

PDF → Image

Standard tool—Ghostscript (gs). Present in most Linux distributions, handles vector graphics and fonts well:

apt install ghostscript

Convert first page to JPEG:

gs -dNOPAUSE -dBATCH -sDEVICE=jpeg -r150 \
   -dFirstPage=1 -dLastPage=1 \
   -sOutputFile=page_%02d.jpg \
   input.pdf

-r150—DPI (150 sufficient for preview, 300 for full quality). -dFirstPage/-dLastPage—page range.

Alternative—ImageMagick via Ghostscript under the hood:

convert -density 150 input.pdf[0] -quality 85 page_0.jpg

[0]—page index (0 = first).

Important: in newer ImageMagick versions (7+), PDF processing via Ghostscript is disabled by default for security. Allow in /etc/ImageMagick-7/policy.xml:

<!-- was: rights="none" -->
<policy domain="coder" rights="read|write" pattern="PDF" />

DOCX → PDF

LibreOffice in headless mode—most reliable free tool:

apt install libreoffice
libreoffice --headless --convert-to pdf --outdir /output /input/document.docx

Conversion takes 2–8 seconds per typical document. LibreOffice creates user profile on first run—parallel calls from different processes conflict. Solution: unique profile per call via --env:UserInstallation:

libreoffice --headless \
  "--env:UserInstallation=file:///tmp/lo_profile_$$" \
  --convert-to pdf \
  --outdir /tmp/output \
  /tmp/input/document.docx

$$—process PID, ensures uniqueness.

PHP Conversion Service

namespace App\Services;

use Illuminate\Support\Str;

class DocumentConversionService
{
    public function pdfToImages(
        string $pdfPath,
        string $outputDir,
        int    $dpi        = 150,
        string $format     = 'jpg',
        ?int   $maxPages   = null
    ): array {
        @mkdir($outputDir, 0755, true);

        $pages    = $this->getPdfPageCount($pdfPath);
        $maxPages = $maxPages ? min($maxPages, $pages) : $pages;

        $outputPattern = escapeshellarg("{$outputDir}/page_%03d.{$format}");

        $cmd = implode(' ', [
            'gs',
            '-dNOPAUSE -dBATCH -dSAFER',
            '-sDEVICE=' . ($format === 'png' ? 'png16m' : 'jpeg'),
            "-r{$dpi}",
            "-dFirstPage=1 -dLastPage={$maxPages}",
            '-dJPEGQ=85',
            "-sOutputFile={$outputPattern}",
            escapeshellarg($pdfPath),
            '2>&1',
        ]);

        exec($cmd, $output, $exitCode);

        if ($exitCode !== 0) {
            throw new \RuntimeException(
                "PDF conversion failed: " . implode("\n", $output)
            );
        }

        // Collect created files
        $files = [];
        for ($i = 1; $i <= $maxPages; $i++) {
            $file = sprintf("{$outputDir}/page_%03d.{$format}", $i);
            if (file_exists($file)) {
                $files[] = $file;
            }
        }

        return $files;
    }

    public function docxToPdf(string $docxPath, string $outputDir): string
    {
        @mkdir($outputDir, 0755, true);

        $profileDir = sys_get_temp_dir() . '/lo_profile_' . Str::random(8);
        @mkdir($profileDir, 0755, true);

        $cmd = implode(' ', [
            'libreoffice',
            '--headless',
            "--env:UserInstallation=" . escapeshellarg("file://{$profileDir}"),
            '--convert-to pdf',
            '--outdir ' . escapeshellarg($outputDir),
            escapeshellarg($docxPath),
            '2>&1',
        ]);

        exec($cmd, $output, $exitCode);

        // Delete temporary profile
        $this->rmdir($profileDir);

        if ($exitCode !== 0) {
            throw new \RuntimeException(
                "DOCX to PDF failed: " . implode("\n", $output)
            );
        }

        $outputFile = $outputDir . '/' . pathinfo($docxPath, PATHINFO_FILENAME) . '.pdf';
        if (!file_exists($outputFile)) {
            throw new \RuntimeException("Output PDF not found after conversion");
        }

        return $outputFile;
    }

    public function getPdfPageCount(string $path): int
    {
        $cmd    = "pdfinfo " . escapeshellarg($path) . " 2>/dev/null | grep 'Pages:' | awk '{print $2}'";
        $output = shell_exec($cmd);
        return max(1, (int) trim($output ?? '1'));
    }

    private function rmdir(string $dir): void
    {
        if (!is_dir($dir)) return;
        $items = new \RecursiveIteratorIterator(
            new \RecursiveDirectoryIterator($dir, \FilesystemIterator::SKIP_DOTS),
            \RecursiveIteratorIterator::CHILD_FIRST
        );
        foreach ($items as $item) {
            $item->isDir() ? rmdir($item->getRealPath()) : unlink($item->getRealPath());
        }
        rmdir($dir);
    }
}

Jobs for Background Processing

// app/Jobs/ConvertDocumentJob.php
class ConvertDocumentJob implements ShouldQueue
{
    public int $timeout = 300;
    public int $tries   = 2;

    public function __construct(
        private int    $documentId,
        private string $type  // 'pdf_to_images' | 'docx_to_pdf'
    ) {}

    public function handle(DocumentConversionService $converter): void
    {
        $doc = Document::findOrFail($this->documentId);
        $src = Storage::disk('documents')->path($doc->path);
        $outDir = Storage::disk('documents')->path("converted/{$doc->id}");

        match ($this->type) {
            'pdf_to_images' => $this->convertPdfToImages($converter, $doc, $src, $outDir),
            'docx_to_pdf'   => $this->convertDocxToPdf($converter, $doc, $src, $outDir),
        };
    }

    private function convertPdfToImages(
        DocumentConversionService $converter,
        Document $doc,
        string $src,
        string $outDir
    ): void {
        $files = $converter->pdfToImages($src, $outDir, dpi: 150, maxPages: 20);

        $pages = array_map(
            fn($f) => "converted/{$doc->id}/" . basename($f),
            $files
        );

        $doc->update([
            'preview_pages' => $pages,
            'page_count'    => count($pages),
            'status'        => 'ready',
        ]);
    }

    private function convertDocxToPdf(
        DocumentConversionService $converter,
        Document $doc,
        string $src,
        string $outDir
    ): void {
        $pdfPath = $converter->docxToPdf($src, $outDir);
        $relPath = "converted/{$doc->id}/" . basename($pdfPath);

        $doc->update([
            'pdf_path' => $relPath,
            'status'   => 'ready',
        ]);
    }
}

Security When Processing Documents

User files—potential attack vector. Mandatory measures:

• Check MIME type via finfo_file(), not just extension.
• Run conversion in separate user without write rights to project root.
• Limit file size (max: 50000 in validation rules—50 MB).
• Don't store uploaded files in public path until check completes.

$request->validate([
    'file' => [
        'required',
        'file',
        'max:51200', // 50 MB
        'mimes:pdf,docx,doc',
    ],
]);

// Additional real MIME check
$finfo = new \finfo(FILEINFO_MIME_TYPE);
$mime  = $finfo->file($request->file('file')->getRealPath());
abort_unless(in_array($mime, ['application/pdf', 'application/vnd.openxmlformats-officedocument.wordprocessingml.document']), 422);

Timeline

Configure Ghostscript, LibreOffice, conversion service, Jobs—6–8 hours. Add PDF page previews to UI, converted PDF download endpoint—another 3–4 hours.