imagemagick handles almost all image files

images ) ls
001.jpg  002.jpg  003.jpg  004.jpg  005.jpg
images ) convert 001.jpg example.pdf

ffmpeg handles almost all video files

ex ) ls
rock.mp4
ex ) ffmpeg -i rock.mp4 rock.avi

if you use gnome there’s a nice little feature of the file explorer where you can just drag and drop scripts into ~/.local/share/nautilus/scripts/

for example

make a fish script (ignoring error checking for brevity here, my real script had a couple guard rails)

#!/usr/bin/env fish
set file $argv[1]
convert $file (basename $file .png).pdf

then when you right click on a file in your gnome file explorer you can click the scripts option

example

and the script is right there so you can just easily convert with the press of a button

example

note, i crossed out some stuff that includes client names

tldr: there are so many ways to do what you need to do there’s no reason to trust random websites you don’t know. there’s a lot of slimey people out there wanting to take advantage of people. and everybody should strive to be at least a little computer literate. the examples i gave here aren’t complicated. they’re simple commands