integrating two asp.net applications with sharepoint portal

We have a web application in .net and workflow engine developed in.net.
And need to integrate these two and updations should reflect on Share point portal .Has any one any clues to implement it? Or have u worked in developing such kind of applications or integrating 2 applications?
When a document is loaded, we should pass it to workflow engine and should be in pending mode once the status of approval or rejection done in workflow engine documents permissions would be given to edit or update by the users of the site. And these status should be updated in sharepoint server .We are storing documents in sharepoint portal'

am I clear??
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