I must developpe a Max/msp patch existing in PD.

Does somebody know if there is a software which makes it possible to convert a file PD into max/msp?

not ever heard of such a thing, no. you can crudely convert max patches to pd with the cyclone library though,

PD allows you to save out patches in a 'max' format - this is in a text format that's a bit different to the pd one.

That would allow you to open them in Max/MSP - but you are likely to get some very...interesting results.

Can you have the 2 programs side by side perhaps - that would be the easiest way I reckon.

A