pdf or epub ? what are good points and bad points ?

> What are the reasons to prefer epub rather than pdf ?

Readable text on screens of various size.

> What are the reasons to prefer pdf rather than epub ?

Printing or complex layout. It also looks the same with all reader
programs (except for ones not supporting embedded fonts or old Adobe
programs).

EPUB is HTML with additional metadata, it's great for simple texts (like
most fiction works that I know) that can be optimally split into lines
for the specific screen size used (and text size preferred by the
reader).

PDF describes specific positions of glyphs (of specific fonts) on the
physically sized page. It's difficult to read it e.g. on a phone screen
(needs much horizontal scrolling or has too small characters), while it
can represent specific layout for e.g. mathematics or advertising texts.

How about FB2? It is very good format, IMHO. You can easily convert many formats of documents to FB2.
And FB2 can be easily converted to PDF, EPUB, etc.
FB2 have text structure, you can read FB2 without any special software.

FB2 is very popular in exUSSR countries.

Thank you for your answers.

I think I will stay with pdf, and because I am learning now how to make tex files (learning LaTeX language).

I use no iPhone or any mobile phone like it.

I didn't know FB2.

FB2 or PDF ? ^^

Thank you, I installed it and will try.

Is EPUB a free format?