To apply a linear fit to all four datasets, you can select all four datasets within your Origin worksheet and select Analysis -> Linear Fit which will produce one analysis sheet for all four datasets.
Regarding the .spec files: Here are a list of third party format files that can be imported into Origin. I don't believe .spec files can be imported into Origin, however please take a look at the list to see if you can use a different file type for importing. https://www.originlab.com/doc/Origin-Help/Import-ThirdPartyFormats