Historia Universal Salvat (20-volume edition) is a comprehensive encyclopedia covering human history from prehistoric times to the 21st century. Where to Find It (PDF & Links)
However, I can offer you a full informational post that explains what the collection is, where to find it legally, and how to access digital copies through legitimate means. historia universal salvat 20 tomos pdf link
Because the work is still under copyright, you will not find a free, legal PDF of the complete 20 volumes on public websites. However, here are your best options: where to find it legally
The Ancient Near East: Exploring Mesopotamia, Egypt, and the Levant. you will not find a free
The World Wars: Global conflicts that reshaped the 20th century.