TOPIC:

i'm sure, the PDF file can edit by demo project.
first click on editbox, background will become yellow, then click on yellow background, will display soft keyboard.
i suspect that you are using your own project to active demo license.
please run demo project without any modification.

Then it's probably due to license. I was testing in my own project.

By the way, i tried replacing my test pdf in your demo project. I can click on form fields but the popup doesn't appears. It just get borders marked with a black line and nothing happens. If i click again then the form is unselected.

do not open the PDF file from Asset, Asset is resource of App, can't be editable.
please rename the PDF file name, and then place on root path of sdcard.
and to sure, no other app is opening this PDF file.

Ok, and it can be edited if i load it from memory or a private app file folder? From sdcard could not be an option for me to avoid publishing this file on a "public" folder.

Ok, and it can be edited if i load it from memory or a private app file folder? From sdcard could not be an option for me to avoid publishing this file on a "public" field.

no, you misunderstood on it.
open from Asset is not open from sandbox, Asset data is zipped data, not exists no storage.
if we open PDF from Asset directly, we just like open it from memory.

if you want edit PDF file from Asset, you have to extract Asset data to sandbox, then open file from sandbox.