Validating paypal transaction ID with PHP?

I used paypal IPN before to add the payments to a database, but now what I want to do is to h开发者_如何学Goave a textbox where I input only a paypal transaction ID, submit the form and know if the transaction ID is from a valid payment or not.

Can this be done?

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Please refer to the SDK http://www.paypalobjects.com/IntegrationCenter/ic_sdk.html