If you download a ZIP or RAR containing a Daz file (IMxxx.zip), you drill down until you locate the file, then you just put the zip file in C:\Users\Public\Documents\DAZ 3D\InstallManager\Downloads.
Next, you open DIM, click on 'Work Offline', and start the cue.
DIM will install the zip and Manifest files normally.
Obviously, since you didn't buy it from Daz, your account won't have any record of the purchase because you 'pirated' the file, just the same as a file from a third party like Renderosity wouldn't show up in your Daz account.
As far as access to the file goes, you'd have to provide more detail (file name, where you put it, etc.). HINT: You should make a new folder to extract files to so you're the folders 'owner', then proceed as above.