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QuickBooks Canada : Pro 2012how many companies can you add under "New Company"? Is there a limit?
how many companies can you add under "New Company"? Is there a limit?

There is no "reasonable" limit.
Are you thinking of something very large?
As far as I know, that's not a problem, but you may run into limits in terms of Items/customers, depending on the QuickBooks version (see the link below). If in doubt, you could call the toll free support number that is listedat the top.
http://quickbooks.intuit.ca/accounting-software/compare-quickbooks-editions.jsp
The limits on the numbers of names, Items, etc. apply to EACH company - not to the combined totals of all companies. 20,000 small companies or 200 large companies should not be a problem.

Each company has it's own data file & I do not believe there is a limit to how many data files you can have on your computer.
(As a bookkeeper I have a lot of data files, my accountants have more!)
There is other software such as PCLaw where the software is licensed to each company with specific users & billing numbers. They don't care how many computers it is on, but there are restrictions to how many lawyers can bill & how many users can access the data at the same time. Quickbooks is not like that - you license your computer and can open (one at a time) as many companies as you wish.
Kate