Q: Problem with Boot Camp not recognising my ISO file?

I am very much a novice Mac user....bought my Macbook a couple of months ago.  Decided to install Windows 7 as I have a lot of applications and data - particularly genealogical stuff - on my PC (which I keep upstairs), I have mobility issues and it would be very convenient to have stuff more conveniently accessible on my Macbook.

I purchased a full version OEM 64 bit Windows 7 DVD from Ebay and printed several pages of advice from the internet, mostly from Apple, explaining the procedure for creating an ISO image with Disk Utility....then Boot Camp Assistant to partition and format the SSD for the Windows 7 installation.

Using a Samsung USB DVD writer I created the .cdr file on which I converted the extension to .iso.  However, when I opened the newly created Windows 7.iso file in Boot Camp Assistant and, leaving ticked all three options in "Select Tasks"  i.e. Create a Windows 7 or later version install disk....Download the latest Windows support software from Apple....Install Windows 7 or later version; and click 'continue' I got the message from Boot Camp saying :- "Your bootable usb drive could not be created - Boot Camp only supports Windows 7 or later installations on this platform....".

Why do I see this when the iso I created is widows 7?

Any advice would be greatly appreciated...many thanks.