We have companies 200 & 300 existing on the same server for the last 8 years. They share some tables (customers, suppliers, and a few others). Management would now like to merge company's 300 data into 200. We would then have only 1 company. Is there any document or guide that can help us with this process? Any advice?

Some advice, from a similar project we did a couple of years ago, where we merged 5 companies into 1...

For data that is number ranged (e.g. order numbers) you will have to dump the table data to an ASCII file, and, using some scripting, change the series to ensure uniqueness. Secondly, it would be easiest to dump both companies, use scripts to merge them, change the company number everywhere it occurs, and load it into a new company, say 400. Also, when creating ASCII dumps, remember that some data fields (especially text fields) may contain special characters, thus be careful when choosing the separator character. You can do everything using Oracle text dumps, with a control character as separator... Lastly: test, test, test and test again! ;)