The Standard edition of Beyond Compare is a powerful full-featured comparison tool, not a stripped-down "lite" version. The Standard edition has full-screen editing, full Unicode support, syntax highlighting and much more.
However, the Pro edition adds these advanced functions:
3-way merging 
Compares independent changes against a common ancestor to create new merged content, for folders or individual files.
Text replacements
Specifies text as unimportant if it is changed to a specific value on the other side. For example, you can make apple found on the left when compared to orange on the right an unimportant difference.
Folder Compare alignment overrides
Overrides how files are aligned in a Folder Compare session. For example, you could compare your .gif files on one side with .png files of the same name on the other side.
Source control integration 
Adds commands for checking files in or out of SCC-compliant version control systems.
SFTP support
Rather than relying on third-party solutions, Beyond Compare Pro has integrated support for secure FTP protocols (SFTP and FTP over SSL).
Registry Compare
Compares live registries, both local and remote, as well as registry files.
Note The trial download of Beyond Compare actually contains both Standard and Pro editions. You can disable Pro mode in the Help > About dialog in order to limit your trial to Standard functionality.
Your license key will unlock the appropriate edition for permanent use. If you choose the Standard Edition license, you can upgrade later to Pro for the difference in price.