then I would like to share the first 25 songs for free by providing a link to it in the sales letter to a YouTube playlist containing the first 25 songs
I'm not quite following.
Let's start with "sales letter." What does that mean? Is this a letter you're going to send to someone? If so, to whom are you going to send it?
Also, you wrote that you want "to share the . . . songs" (
plural) "by providing a link to
it." To what does "it" refer? Are you saying you're going to send someone a list of links to videos on YouTube?
(songs that are already freely available on YouTube)
Just because something is on YouTube doesn't mean it's there with the permission of the appropriate rights holders.
The list of music in the PDF
I assume you mean the list will be in the PDF (since you can't put music in a PDF).
the PDF that I want to sell would also contain a link after every title that refers the person to the music video of that song (that is also already freely available on YouTube), I would like to know if such a thing would be legally possible
If all you're doing is distributing a list of links to stuff that is legally on YouTube, that's not a problem. I do, however, have to wonder why you'd think anyone would pay for that.