open random pdf file from folder with coding (HTML main code used)

I have made this website where I collect recipes I can eat.

I would like to add a 'random' feature, where one of the recipes opens and I don't have to chose what to eat.

My knowlege of coding is limit (like a year of highschool making a HTML website limited) but I do now it has to be possible. I also learned very briefly about a random number generator option in PHP and Javascript.

The website is coded with HTML and Notepad++.

The files are all pdf typed and like this, '1.pdf' '2.pdf'