Principle bundle
Foundations of Differential Geometry vol 1 - Kobayashi, Nomizu.pdf
http://tomlr.free.fr/Math%E9matiques/Math%20Complete/Differential%20Geometry/Foundations%20of%20Differential%20Geometry%20vol%201%20-%20Kobayashi,%20Nomizu.pdf
(same PDF)
Foundations Of Differential Geometry Vol 1 Kobayashi, Nomizu Pdf | Al-Zaytoonah University
https://www.zuj.edu.jo/download/foundations-of-differential-geometry-vol-1-kobayashi-nomizu-pdf/
(vol. 2)
Foundations of differential geometry Vol.2 (Wiley,1996)(ISBN 0471157325)(Kobayashi S.,Nomizu K.)(485s).djvu - Kobayashi_Nomizu_II.pdf
https://www.fuw.edu.pl/~suszek/pdf/Kobayashi_Nomizu_II.pdf
Kähler manifold
Complex Geometry-An Introduction (Universitext).djvu - Huybrechts-Complex_Geometry.pdf (from p. 113 or p. 123 in the PDF)
http://www.im.ufrj.br/~andrew/ensino/VC20-1/Huybrechts-Complex_Geometry.pdf
ComplexGeometry.pdf (by Weiyi Zhang, not published)
https://homepages.warwick.ac.uk/staff/Weiyi.Zhang/ComplexGeometry.pdf
Harris_AlgebraicGeometry.pdf (It is uncertain that the Kähler manifold is explained but apparently useful.)
https://userpage.fu-berlin.de/aconstant/Alg2/Bib/Harris_AlgebraicGeometry.pdf
probably original paper
Über eine bemerkenswerte Hermitesche Metrik - BF02940642.pdf (Hamburg, den 22. Oktober 1932)
https://link.springer.com/content/pdf/10.1007/BF02940642.pdf
Fiber bundle
Historical
manifold.pdf (Differentiable manifolds, Hassler Whitney)
https://www.maths.ed.ac.uk/~v1ranick/papers/manifold.pdf
pnas01759-0054.pdf (Sphere-spaces, Hassler Whitney)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1076627/pdf/pnas01759-0054.pdf
Topologie Dreidimensionaler Gefaserter Räume (H. Seifert, in German)
https://projecteuclid.org/journals/acta-mathematica/volume-60/issue-none/Topologie-Dreidimensionaler-Gefaserter-R%c3%a4ume/10.1007/BF02398271.full
