Synching notes on Pdfs between devices

Hi everyone! I have many .pdf files in my iCloud folder. Some are books and some are academic articles. On both I underline, take notes, mark things I need to remember, erase other parts and so on. I am looking for a solution that will let me study those files on a device (say my iPad) and than, later in the day, find that very file (with all the annotations that I've made on my iPad) on my mac. Basically I want the files to be synched on all my device. I tried out iBooks from apple but i can't always do what I need, sometimes I can't even underline at all. Il like pdf expert, but when I transfer files from my mac to my iPad through iTunes file transfer I don't know how to put them back on my mac once I have studied them. I love Mendely pdf manager but when it come to synching, having more that 10gb of pdf file, it becomes quite expensive (15 € per month). Since I have bought iCloud storage is there a solution involving such additional space I have purchased? As always, thank your time! Fulvio