I don't know if this is a problem with MTS older files, or maybe it's a virus on my computer? I'm trying to re-install the game afresh and am downloading the old favorite basic mods. Several of the zips I downloaded contain pdf instruction files, but the actual program files are missing. Am I just being stupid with this or is there really a problem?
Examples
Shadow fix https://www.modthesims.info/d/56958...d-2-jan-16.html
Moo's Subhood selector https://modthesims.info/d/420924/fi...-selection.html
GunMod's Camera http://modthesims.info/d/97642/gunm...e-versions.html (used scriptorium to get around this)

Just downloaded Moo's mod to see and zip file contains 4 package files and no pdf. Try unzip into a folder.

Annaminna, thank you. That's a format problem then. I'll see if updating WinZIP will help.

I'd try using a different program like 7zip, maybe. I haven't had the best track record with WinZIP.

files are OK, they're compressed with standard zip/gzip compression type, which is even present in Windows since W7 (?). Just unpack them either by any zip-compliant program or by Windows' functionality.

With difficult files, it's sometimes best to save the zip file, then right-click it and open with an unzip program. You can drag-and-drop files from there to where they are supposed to be.

Sometimes it's the format that's buggy, other times an unrelated program has for some reason decided it's the proper program to open such files in (even if it's not), and things get a bit messy (like when you extract a file and it suddenly pops up in SimPE, or some such). Could be it's just the wrong icon, but the format is correct (for instance looks like a PDF icon, but is actually a package file)

If you continue running into the problem after trying 7-Zip, check any security programs (antiviruses, etc). Some of them can get a little aggressive at times.