Many online guides will tell you to from shady DLL websites. Do not do this. That is almost always a scam or a vector for malware.
ISDONE.dll & UNARC.dll Errors: What They Are and How to Fix Them (No Download Required) isdone.dll error unarc.dll download
If you’ve ever tried installing a large PC game or software and got hit with a popup saying: “An error occurred while unpacking: Unable to execute unarc.dll” or “isdone.dll returned an error code,” you know how frustrating it can be. Many online guides will tell you to from shady DLL websites