type格式(fileType)：

Generic AutoCAD drawing

NOTES on AutoCAD file headers: The 0x41-43-31-30   (AC10) is a generic header, occupying the first four bytes in the file. The   next two bytes give further indication about the version or subtype:

0x30-32 (02) — AutoCAD R2.5

0x30-33 (03) — AutoCAD R2.6

0x30-34 (04) — AutoCAD R9

0x30-36 (06) — AutoCAD R10

0x30-39 (09) — AutoCAD R11/R12

0x31-30 (10) — AutoCAD R13 (subtype 10)

0x31-31 (11) — AutoCAD R13 (subtype 11)

0x31-32 (12) — AutoCAD R13 (subtype 12)

0x31-33 (13) — AutoCAD R14 (subtype 13)

0x31-34 (14) — AutoCAD R14 (subtype 14)

0x31-35 (15) — AutoCAD R2000

0x31-38 (18) — AutoCAD R2004

0x32-31 (21) — AutoCAD R2007