I've found an older self-written extension (.avx) for ArcView 3.2 from a retired co-worker. Unfortunatly I'm not a programmer, but I'd like to use this extension for ArcMap 9.3. or 10.x. Is there any way to import/convert this extension?
Unfortunately, the answer is 'no'. Extensions for ArcView 3.x are written in the Avenue language, which ArcGIS has never supported.
The only way I can think of is to completely rewrite the code in .Net or Python. If the extension is not encrypted you may be able to extract the original code, otherwise you need to have an instance of ArcView 3 running, or find a decryption tool (can't find it right now, but I think there used to be one)