Was wondering if doujinshi can get an anime adaptations and become real manga that are officially sold by companies.
If by "doujinshi" you mean "self-published manga that parody other published works" (probably the most restrictive definition), the answer is yes. Examples:
- Nyoron Churuya-san (a Suzumiya Haruhi no Yuuutsu doujin)
If you loosen the definition to "self-published manga", there are even more examples:
- Sore ga Seiyuu!
- Getsuyoubi no Tawawa
If you go further and consider all self-published works (including webcomics and text-only media), there are even more:
- Maoyuu Maou Yuusha (originally a series of posts on 2ch)
- Isekai wa Smartphone to Tomo ni (originally posted on "Shousetsuka ni Narou")
- Re:Zero (likewise)
- One Punch Man (originally a webcomic)
This is by no means a rare phenomenon. Self-published stuff that becomes popular gets commercialized pretty often.
Example: Yoshitoshi Abe's, Haibane Renmei.