Pink Elephant, ehrt74
Thanks for the advice.
Quite simply, my problem is solved.
My problem was that I could not open PDFs in Evernote.
Pink Elephant told that when I tap on the PDF, gets a blue outline, but my problem was that I couldn't even get that outline to appear.
I was using the legacy version of Evernote because I was having trouble using the lastest version. I just upgraded to the latest version and now I can open PDFs.
To be honest, with each version upgrade, the Evernote software is getting harder to use, but I can't do without being able to open PDFs. This time I give up to upgrade.
Thank you all for your answers.