>Are there any enhancements in VFP 9.0 regarding database security or tables are still visible and can be opened in excel?
>Should we expect any problems converting our applications designed in VFP 7.0 to VFP 9.0.?


As Sylvain said, there is no change in dbf structure or security.
As for compatibility, it is very good. You should not expect any major trouble converting, as long as you follow the advice of the help files in a few issues.

SQL GROUP BY changes to make it more ANSI-92 compatible
See SET ENGINEBEHAVIOR

A few things like validation have been tightened. Look at SET TABLEVALIDATE.
Menus can have images. There are new field types that will make your tables not backward-compatible if you use them.

But all in all your VFP 7.0 programs should compile and run fine.