PL/SQL starts out as ASCII text files. Then you compile that source code into the database. Once it is there you can inspect what has been compiled. The old school way to do this is to inspect the USER_SOURCE view. Specifically you can query the TEXT column. It has your source code.
There are more advanced ways to check up on the code in the database. The SQL Developer tool has a function to search PL/SQL source code. You can also check out the ALL_ARGUMENTS view. It has parameter information for packages.
One setting that helps control your ability to analyze source code is PLSCOPE_SETTING. This can be set at either the session of system level. This allows you to analyze identifiers. You access this data using views such as ALL_IDENTIFIERS. Finally there is the DBMS_METADATA built in package. You can use it to get object definitions. The output is in XML format. Enjoy.
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