Where can I buy raw manga in PDF format? I'd like to purchase the original Japanese manga in digital form but prefer in PDF format as I don't want to be tied down to using a particular website or even losing my purchased manga (I remember buying a digital manga a couple years ago but when I logged into my account recently it was no longer there.)
As far as I know, there are no raw, digital manga being sold in PDF format. You can convert them, however, using applications found in the Internet. Here are some sites I found that sell raw, digital manga (and there are more mentioned in the forum links I posted below):


https://booklive.jp
https://www.ebookjapan.jp/ebj/
https://www.cmoa.jp
https://books.rakuten.co.jp/e-book/
https://sokuyomi.jp
https://bookwalker.jp
https://honto.jp
https://www.amazon.co.jp


Where I found those sites above: 


https://www.reddit.com/r/manga/comments/3ekjyj/sites_to_buy_raw_manga_from/
https://www.reddit.com/r/LearnJapanese/comments/212get/is_there_a_way_to_buy_legal_digital_copies_of/
https://www.reddit.com/r/manga/comments/7hg7i6/best_legal_japanese_ebook_sites_for_raw_manga/