I had to download adobe so I could follow along with some instructions if found (will try to add the link)
I copied the file , opened the copy
clicked on the black box and moved it
flag{rememb3r_t0_flatt3n_ur_PDF5}
orginal writeup at https://medium.com/@prince0f4llsaiyanz/tenable-ctf-2022-babby-web-1-2381da94f29e