Im stumbled with this problem. Im merging multiple PDF-files into one depending on what PDF's the client choose.
If i choose the smallest size PDF's and merge it works fine but as soon as its a lil bigger, like around 1MB i get Fatal error: Allowed memory size of xxxxxx bytes exhausted (tried to allocate xxxx).
I know its a php.ini problem, just put it higher but i cant change it unless i pay for a bussniess account...
Is there any workaround, like lower the PDF quality size then higher it again? I really don't know what to do :S
You can try it yourself here: pdf.devharis.com
Choose the cheapest two and order them..., then try some bigger it crashes...