Requirements < v7.0

mPDF requires a minimum of PHP 4.3.10 or PHP 5.0.3

mPDF v5.7.1 minimum is required for PHP ≥ 5.5

(Since version 1, mPDF has been developed on PHP5 only, but should still be compatible with PHP ≥ 4.3.10)

PHP requires the mb_string module to be enabled (including mbregex, which needs to be explicitly enabled in some environments)

mPDF is not compatible with PHP function overloading (mbstring.func_overload)

As for FPDF, PHP requires zlib for compression.

Improved performance requires write permissions to the temporary cache folders.