Watermark not showing up in pdf

Hello

I am trying to use Your plugin (free) but it doesnt work ?? I try with several different pdf files and it works with all execpt the one i need :/ – watermark didnt show. Can be any other reasons excepting these You write in woocommerce instructions ? Pdf has 120 pages

Pdf is 1.4 version, size 5,83 x 8,27 inch make in FPDF 1.81