The main difference between of AppCheck Pro and Free version is below.
1. Automatic Remediation and Block
AppCheck Free only blocks and kills the process while AppCheck Pro blocks and deletes(remediates) the detected Ransomware behaved files.
Automatic recovery of damaged files are both supported.
2. Network Drive and SMB Server Protection
AppCheck Pro provides protection of Network Shared folders. Any file damage or encryption behavior to attached shared folder will be detected and blocked. Especially SMB Server Protection provides protection against unwanted file change of current host's shared folder.
3. Auto Backup
AppCheck Pro provides additional protection through flexible scheduled backup of user specified folder or files.
More details and comparison chart can be found in this page.