Sites like NSPortal or All-fof-edu sometimes host educational scans for teachers and students.
Analysis of different styles, from folk and opera to contemporary pop. How to Download (Skachat)
Older pedagogical texts may be available for free on sites like Archive.org . g., for a child or a professional student)?
Many "Vse o Muzyke" books are illustrated encyclopedias for children and students. They cover musical notation, famous composers like Bach and Tchaikovsky, and the evolution of musical genres from classical to jazz and rock.
To find a digital copy, you can look through these types of platforms:
Descriptions of orchestral families (strings, woodwinds, brass, percussion) and modern electronic instruments.
Websites like Litrres (Литрес) or MyBook often have these titles available for legal purchase and download in formats like PDF or EPUB.