File Type	Header (Hex)	Header (ASCII/Unicode)
png	89 50 4e 47	‰PNG
jpg	FF D8 FF E0	ÿØÿà
bmp	42 4D	BM
avi	52 49 46 46 xx xx xx xx 41 56 49 20 4C 49 53 54	RIFF.... AVI LIST
wav	52 49 46 46 xx xx xx xx 57 41 56 45 66 6D 74 20	RIFF.... WAVEfmt
mpg (video)	00 00 01 Bx	....
doc, ppt, xls	D0 CF 11 E0 A1 B1 1A E1	ÐÏ.ࡱá
mp3	FF Fx	ÿ.
pdf	25 50 44 46	%PDF
docx, pptx, xlsx, zip	50 4B 03 04	PK..

(Note: x is used as a wildcard, meaning any hex value can be put where an x is found and not impact the file header)