CAD tip # 868:

You can use the Find Files function in Windows (Start button). Enter *.DWG as file name in the Advanced tab enter text:

• MC0.0 - DWG from Rel. 1.1
• AC1.2 - DWG from Rel. 1.2
• AC1.4 - DWG from Rel. 1.4
• AC1.50 - DWG from Rel. 2.0
• AC2.10 - DWG from Rel. 2.10
• AC1002 - DWG from Rel. 2.5
• AC1003 - DWG from Rel. 2.6
• AC1004 - DWG from Rel.9
• AC1006 - DWG from Rel.10
• AC1009 - DWG from Rel.11/12 (or LT R1/R2)
• AC1012 - DWG from Rel.13 (or LT95)
• AC1014 - DWG from Rel.14, 14.01 (or LT97/LT98)
• AC1015 - DWG from AutoCAD 2000/2000i/2002 (or LT, Map or relative Desktop version)
• AC1018 - DWG from AutoCAD 2004/2005/2006 (or other product in the "2004", "2005" or "2006" family)
• AC1021 - DWG from AutoCAD 2007/2008/2009 (or other product of the "2007", "2008" and "2009" families)
• AC1024 - DWG from AutoCAD 2010/2011/2012 (or other product of the "2010", "2011" and "2012" families)
• AC1027 - DWG from AutoCAD 2013/2014/2015/2016/2017 (or other product of the "2013", "2014", "2015", "2016" and "2017" families)
• AC1032 - DWG from AutoCAD 2018/2019/2020/2021/2022/2023/2024/2025 (or other product of the "2018" to "2025" family)

There are also other, internal file versions: AC1001=pre-2.5, AC1005=pre-R10, AC1007=pre-R11, AC1008=pre-R11, AC1010=pre-R13a, AC1011=pre-R13b, AC1013=pre-R14, AC1500=pre-2000, AC402a=pre-2004a, AC402b=pre-2004b

You can also text-view your DWG file and look at the string at the beginning of your file. Or you can use the DWGinfo utility available at Download. See also the DWGintVer utility - Download.