I will be very grateful to receive free course or teaching material (can be in pdf) that teaches electronic calculations in the area of analog and digital electronics, oscillators using operational, relaxation oscillator, etc. Preferably in PDF so I can translate. Grateful.

Why don’t you look first on “The Art of Electronics (2nd Edition), by Horowitz & Hill”. You could find it anywhere on the internet or buy this edition on Amazon.

As for the more “complex and heavy” literature, I am sure that the Web is so big, that Google itself could give thousands of .pdf files, including special courses from Carnegie, MIT (free OpenCourseWay), CalTech, etc. Not counting the numerous Academic Libraries with tons of E-books, tutorials and other resources in electronics.