Edit Errors

I am quite frustrated and confused as I have just downloaded the ADOBE 20.11.00 Paying $16 per month and I have tried to just edit a PDF file from my drop box account. 
It reads 'double click to edit' or similar words. 
I do double click just as you or ally would to edit a PDF and it completely changes the format every single time.
Please help!

I am using an IPad Pro Latest version 2020