At some point in the development for security purposes, I needed to parse PE format in the header of executable to get information about sections, Is doing that fine? or it's something should be avoided since many parts aren't officially documented? Thanks in advance.
Regarding sections, IMAGE_SECTION_HEADER is unlikely to change much in future. The Microsoft PE file format is well-documented and Microsoft is not likely to introduce breaking changes to the format itself. (The core of the format, including the section structures, has not changed significantly in over 25 years.) Unless you are dealing with extremely niche situations, it should be fine to rely on the existing spec to write your code.