I'm looking for a way to save PDF on Ipad (or in the cloud) and name (or even tag) them.

If you install the iOS Dropbox app, it will put a very convenient "Save to Dropbox" as an option in the share options (the box with the up arrow). Any page in the browser you can save as a pdf (the default). It captures an html page and converts to pdf flawlessly. If you have an existing pdf just upload it directly through the "share" box, will recognize your pdf file and just upload it to whatever you have set as your default folder in the Dropbox app.

Oh, I forgot...yes...you can save a pdf *from the web* with one quick click using the DB app. You can also rename it if you want.

For your tagging purposes, Magenda, you may want to take a look at Together, which is a very powerful information management app. Like the Dropbox app mentioned by Donovan, you can save PDFs to Together (in iOS and in macOS), and it syncs effortlessly between both platforms (now that they've solved their rather iffy early sync efforts). It's a very capable app, not least because it also supports notes and, most recently, checklists

And, similarly, DevonThink To Go.