loanwords - Katakana words with Kanji. How did that happen?

Some words are written with katakana, but also have kanji. For example:

• コーヒー　珈琲


• ページ　頁

How did this happen? They are loanwords, but no doubt had Japanese equivalents before these variants were imported. Is that the case? And are these original words now forgotten?

Answer

had Japanese equivalents before the English variants were imported

Coffee is not native to Japan, and did not have an equivalent; that kanji sequence is ateji.

"Page" is that kanji, but it's properly pronounced 「けつ」 in sequences.