I have a bootable usb drive, I want to convert it into iso file again.
How should I do this?
Please help.

used to be remastersys.
it's unmaintained now, but last thing i heard is people are still using & recommending it.

if you need more help, provide more information (see first link in my signature).

You might indicate which distribution of Linux you are using. The recommendation above for remastersys will probably work on Ubuntu and derivatives and the Debian version might also. Otherwise, you might be able to use mkisofs or genisoimage commands to do it but more information would be needed to get useful advice.

in retrospect i'm not even sure i understood the question.

can you explain better what you are trying to achieve, unclesamcrazy?

I'm guessing you have a bootable disk image kind of USB stick & you want to wipe it so you can store ordinary files on it???
If so, the answer is easy - but you need to confirm what it is you want to do.

A cd or dvd live cd has a few features.

One is they tend to use a compressed filesystem like squashfs. That file may still be on your usb depending on how you created it.

Two is some feature that loads or starts like syslinux or other. Generally grub isn't used on an optical media.

If one makes a distro the last step they do is run a program like mkiso or something like that to mash it all together.

Thanks for replying on my question.

I created a bootable pendrive of windows seven from windows seven iso file using a software. Now windows 7 is installed successfully on the laptop for which I created bootable pendrive but I lost the iso file. Now I have only this working bootable pen drive of windows 7 but I can not keep the files this way. I need to use the pendrive for other purpose too.

I tried to create iso from the files of the pendrive on my ubuntu using command
It creates an iso file but when I try to create a virtual machine in vmplayer, it shows error "operating system not found"

I was not getting this error using my old iso file.
How can I create working iso file so I will be able to boot win7 in KVM, VMplayer or virtualbox.

Please Help.

The command you posted will never work to boot an iso file because you did not enter any boot parameters. Also, you never mentioned that this was a windows iso you want to create which makes a difference so I would suggest you do an online search for how to do this in windows 7.

http://forum.imgburn.com/index.php?showtopic=11194

Microsoft doesn't allow you to use windows 7 on a usb by it's eula unless you have a very special agreement with them.