How can PHP be used in conjunction with shell_exec() to edit PDF files effectively?

To edit PDF files effectively using PHP and shell_exec(), you can use a command-line tool like pdftk or Ghostscript to perform various operations such as merging, splitting, or adding watermarks to PDF files. By executing these commands through shell_exec() in PHP, you can automate the process of editing PDF files.

// Example code to merge two PDF files using pdftk
$pdf1 = "file1.pdf";
$pdf2 = "file2.pdf";
$outputPdf = "merged_file.pdf";

$command = "pdftk $pdf1 $pdf2 cat output $outputPdf";
shell_exec($command);