Hi,
i want to change icon for only one pdf file, not for all pdf! Even better is if i could change the icon only for the panel where i put the file link.
How could i do that?

Thanks all

You don't, but you can create a desktop service file that opens a specific link. And this service file can have about any icon.

In dolphin, create a new "Link to location", pass the location of the pdf there (warning: the link will be dead once you move the file!)
Afterwards edit the file properties. You can just click the icon in the upper left of the dialog and change the icon.

You may then move that link whereever you want, but if you ever move the linked pdf, you'll have to edit the link (it's NOT a symlink) to update the path.

Ok this work in dolphin, but when i put these link to location in panel they take the .desktop-file icon.
My goal is to have a side panel with all my cheat sheet and book-to-read icons, obviously if the icons are all the same it's quite difficult to use the panel.

nobody can help?