@hathemi, it seems to me that you have posted before on this general topic. I suggest you review the replies you received at How can i append to PDF file in Node-Red? and Store data in pdf file. You may have exhausted all the help this group can offer.
My final suggestion is that you find a file translator or pipeline of translators that does the job for you and invoke it from an exec node. You can test it from the command line first. File permissions aside, anything you can do from the command line you can do from inside node-RED. (Apologies to @TotallyInformation. I posted before reading his comment.)
