step 1:Download and install the Windows 7 USB/DVD Download tool
Tool to create a copy of an ISO onto a USB or DVD。
https://www.microsoft.com/en-us/download/details.aspx?id=56485
step 2:download and install Microsoft .NET Framework v2
Windows 7 USB/DVD Download tool base on .NET Framework v2
The following applications must be installed prior to installing the tool:
•Microsoft .NET Framework v2 must be installed. It can be downloaded at http://www.microsoft.com/downloads/details.aspx?FamilyID=0856EACB-4362-4B0D-8EDD-AAB15C5E04F5&displaylang=en.
•Microsoft Image Mastering API v2 must be installed. It can be downloaded at http://www.microsoft.com/downloads/details.aspx?FamilyId=B5F726F1-4ACE-455D-BAD7-ABC4DD2F147B&displaylang=en.
step 3: install and run Windows 7 USB/DVD Download tool
step 4: browse and select E:\software\Windowsserver2012R2ISO.iso
step 5:select create bootable and flash usb disk.
now usb disk can bootable like dvd disk.
A tutorial on using a USB flash drive to install Windows 7
https://www.lifewire.com/how-to-install-windows-7-from-usb-2626264
How to Create a Bootable Windows 7 USB Flash Drive
https://techverse.net/how-to-create-a-bootable-usb-pen-drive-for-windows-7/