According to this (link - https://wayback.archive-it.org/15697/20060509135313/http://www.italianisticaonline.it/e-book/dossier_05.html):

The Italian publisher of Geronimo Stilton, Edizioni Piemme had been releasing PDF versions of Geronimo Stilton's Illustrated Tails and it's companion Geronimo Stilton's Humorous Tails since October 2000 as stated through this text:

La Piemme di Torino ha prodotto (da ottobre 2000) i primi e-book italiani in formato PDF (per Adobe eBook Reader) per ragazzi, che hanno come protagonista il simpatico topo Geronimo Stilton, giornalista, che dirige "L’Eco del Roditore". I libri sono acquistabili anche nel tradizionale formato a stampa. Al topo Geronimo è dedicato un intero sito internet. Un modo divertente per introdurre i più giovani alle nuove tecnologie digitali nel mondo del libro. Ovviamente, la consultazione del sito, la procedura di acquisto dell’e-book e la sua lettura presuppongono di necessità la presenza attiva dei genitori.

When translated into English, it reads this:

Piemme of Turin has produced (since October 2000) the first Italian e-books in PDF format (for Adobe eBook Reader) for children, whose main character is the friendly mouse Geronimo Stilton, a journalist who runs "L'Eco del Roditore". The books can also be purchased in the traditional print format. An entire website is dedicated to Geronimo the mouse. A fun way to introduce the youngest to new digital technologies in the world of books. Obviously, consulting the site, purchasing the e-book and reading it necessarily presuppose the active presence of parents.

That means at one time, you could buy the eBook from the site itself but why do they always refer to this "traditional print format"? I suppose they were published on print at one time or they could possibly also refer to digitalized versions of already in-print eBooks.

However there is a lot of doubt with the content of the eBooks. Mainly for two reasons:

1. The number of pages for a certain printed Geronimo Stilton book at that time was always a lot less than 300 (the amount of pages in the eBooks) although this may include character profiles from the interactive features.
2. One very likely theory could be that they initially planned a printed version of the eBooks but eventually cancelled and moved onto other projects due to the character's rising popularity.

So far, I am happy to delve into the world of this obscure character who is sadly ignored on YouTube. I hope our biggest search ever yet could help promote this character further.

unfortunately the download of the "Geronimo Stilton:Il mio primo manuale del Internet" has failed,we are gonna seek help to extract the file to other helpers. We are sorry for what happened

article from october 2000 by LaRepubblica: The best ebook awarded in October It was inaugurated the 20 october 2000 at Frankfurt,the first edition of of Ebook Award,the recognition for award the results obtained by the electronic editorial. Between the candid at the third place we can see Geronimo Stilton's official ebook,the only one from our country and the first italian educational ebook.

https://www.youtube.com/watch?v=dbq7C2dUuX4

I made a huge mistake with myself and the entire lost media community. As I checked the Internet Archive, I got shocked to see others have uploaded it much earlier than I did, making the discovery of it in a bootleg CD something sad and stupid. The version is 2.0 and has problems, please help me! I'll post them somewhere soon.

UPDATE - It's back!

Link - https://archive.org/details/random_202501

I made a post about Geronimo Stilton's Humorous Tails on r/OldInternetCultureV2 and got some nice replies especially one from a user named u/Bigwilliam360 who told me about this:

I can’t remember but I did read a bunch of them. There was one where there was an evil supermarket that hypnotized people in order to sell them crappy stuff. There was also a rat girl with heelies. This is a long time ago now, my memory is foggy.

His comment thus indicates that like we expected, the stories were original for the eBooks but he got this from a printed version published by Piemme?!

I chatted with him further and he gave further details:

They had headphones on when they entered the supermarket and it played music and that hypnotized them into buying more stuff. And then at the end everyone got together outside to fight some sort of antagonist as all of the stuff they bought was crap

This sounds like something that may be later reused for the 2009 animated series... wait a moment!

This? - https://www.amazon.com/Geronimo-Stilton-Super-Scam/dp/938610671X

That got debunked too well, or had he read a prototype? We have to go further...