When I started sequencing Beethoven's piano sonatas, I used to download the scores from a free download site called IMSLP and print them out. However, there were occasional discrepancies between my scores and my musical advisor's comments. In the course of our correspondence, I found out that it was because of the difference in the sheet music I was using. I was not aware of this, but I was doing it poorly. After that, I purchased the Henle edition of Beethoven’s complete piano sonatas (in two volumes), which is well known as the Urtext edition, and now I use it while referring to it. It is said to be the authoritative original edition that every music student uses. It is said to be "the most faithful edition to the original and the most reliable source edition that preserves the composer's own intentions, compiled based on studies of autographs and first editions by researchers and renowned experts.
However, it is also very thick ( 5 cm together) and very heavy. So I was thinking of scanning only the necessary parts, converting them to PDF, and printing them out for use. However, when I visited the Apple Store at the end of last year, I found an app for iPad called "Henle Library". The Henle Library includes this Henle edition of the Piano Sonatas. When I displayed it on my iPad Pro 12.9inch, I could view it in almost the same dimensions as the sheet music. I decided to use it for a while because I can write on it. But I have a feeling that I will go back to paper soon!