Hi Kate,
You can import adjustments from File > Import > Adjustments in IC. You just need to setup the template to match your spreadsheet. The format selection box seems to indicate that you are able to import excel files from Version 2.1 to 5, though it may also work with more recent versions of excel.
But if you are looking at this for the purpose of updating stock qties after doing an inventory count, you should be using the process in Transactions > Physical Inventory.
You can first print out the Physical Inventory worksheet to an excel spreadsheet and then once you've entered the actual counts you can import it in File > Import > Physical inventory worksheet.
This is of course an abreviation of the process, but we've done this with a number of clients with no major headaches.
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Ryan Brohman
Kitchener, ON