a PC can only have 4 primary partitions
Primary is a keyword here.
If you partition a disk (not a PC, a disk) with the MBR scheme then you can have up to four primary partitions. Or you can use up to three primary and an extended partition (and a dozen more partitions if you desire in the extended part).
If the PC is modern enough then it will also recognise the GPT partition scheme, which allows significantly more than four partitions.
I don't have the the Windows 7 disk
An installation DVD or an ISO image is easily obtained. That is not a problem.
and my friend told me Microsoft will not honour the old license.
But this is.
Getting windows reinstalled it not hard. Getting it legally might be. You say the PC already has windows 7 on it, which means that either:
- The license on it is granted to the office. They probably removed the PC from the inventory, are no longer paying license fees and you are not allowed to use the current installation any more. This is likely for very large offices where program and OS usage is tallied quarterly and then forwarded to Microsoft.
- Or you have a legal version and I see no reason not to
recover the license key and do a clean installation.
Having said that: Always reinstall a computer which you get from an outside source.
This might not be that important to you if you just want to use it as an MP3 player without network connection or something similar which requires no safe setup. But if you ever do internet banking or on-line shopping you want a known clean system. That means a full wipe and reinstallation (after recovering the key).