Before doing anything, copy your entire ACT! database folder (containing .ADF and .PAD files) to a USB drive or secondary folder. Unlocking can sometimes corrupt file headers.
Browse to your .PAD file. The best V600 tools will automatically locate the associated .ADF file. act unlock tool v600rar best
Assuming you have found what appears to be the best version of act unlock tool v600rar, follow these steps: Before doing anything, copy your entire ACT
Most unlock tools manipulate registry keys and process memory. Your antivirus will likely quarantine it. Add the folder to your AV exclusion list before running. Before doing anything