Acrobat 3.0 And Later option uses a low encryption level (40-bit RC4), while the other options use a high encryption level (128-bit RC4 or AES, or 256-bit AES).

• Acrobat 3.0 and later: Uses low encryption (40-bit RC4). Acrobat 5.0 and later: Uses high encryption (128-bit RC4).
• Acrobat 6.0 and later: Uses high encryption (128-bit RC4). This option lets you enable metadata for searching.
• Acrobat 7.0 and later: Uses high encryption (128-bit AES). This option lets you enable metadata for searching and encrypt only file attachments.
• Acrobat 9.0 and later: Uses high encryption (256-bit AES). This option lets you enable metadata for searching and encrypt only file attachments.

An earlier version of Acrobat cannot open a PDF document that has a higher compatibility setting. For example, if you select the Acrobat 7.0 And Later option, you cannot open the document in Acrobat 6.0 or earlier.

Ensure that the compatibility level is consistent with the PDF compatibility level for the same source. For example, if you have a watched folder configured to use the Standard PDF setting (which is compatible with Acrobat 5.0 or later), your security compatibility level must not be higher than Acrobat 5.0.

file2pdfconfig Schema