What is the English of "公文袋"??

應該是 manila envelope (manila 一字有人用大寫, 亦有人不用, 無需太過執著). 用 brown envelope 本來也可以, 因為最初的 manila envelope 是由一種叫 Manila hemp 的纖維製造的 (亦所以叫 manila), 而顏色正是啡色的 (brown). 但當然, 現今除了啡色外, 白色的公文袋亦相當普遍, 所以用 manila envelope 較適合. (事實上, 要說一個啡色的公文袋的話, 是有人會說 brown manila envelope 的.)
至於 manila folder 則多數是指 "文件夾" 了. 要詳細解釋倒不如看圖吧:
manila envelope: http://images.google.com/images?hl=en&lr=&safe=off&q=%22manila%20envelope%22&ie=UTF-8&oe=UTF-8&sa=N&tab=wi
manila folder: http://images.google.com/images?svnum=10&hl=en&lr=&safe=off&q=%22manila+folder%22

2006-12-14 14:29:07 補充：
For those who still think it should be called manila folder please look at the links!! Even the product calling itself a manila folder in the other answer is just a high-end manila envelope!!

brown envelope

你是指file嗎?