Here you can download the official Windows 8.1 ISOs for free.
Windows 8.1 is a release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on August 27, 2013, and broadly released for retail sale on October 17, 2013, about a year after the retail release of its predecessor, and succeeded by Windows 10 on July 29, 2015. Windows 8.1 was made available for download via MSDN and Technet and available as a free upgrade for retail copies of Windows 8 and Windows RT users via the Windows Store. A server version, Windows Server 2012 R2, was released on October 18, 2013.
Download Windows 8.1 Core/Pro x86 ISO:
Architecture: x86 (32-bit)
File Format: ISO
Download: Archive.org
Download Windows 8.1 Core/Pro x64 ISO:
Architecture: x64 (64-bit)
File Format: ISO
Download: Archive.org
Windows 8 / Windows 8.1 Keys:
Windows 8 (Core): FB4WR-32NVD-4RW79-XQFWH-CYQG3
Windows 8 Pro: XKY4K-2NRWR-8F6P2-448RF-CRYQH
Windows 8 Pro incl. Media Center: RR3BN-3YY9P-9D7FC-7J4YF-QGJXW
Windows 8.1 (Core): 334NH-RXG76-64THK-C7CKG-D3VPT
Windows 8.1 (Core-Single-Language): Y9NXP-XT8MV-PT9TG-97CT3-9D6TC
Windows 8.1 Pro: XHQ8N-C3MCJ-RQXB6-WCHYG-C9WKB
Windows 8.1 Pro incl. Media Center: GBFNG-2X3TC-8R27F-RMKYB-JK7QT
Windows 8.1 Enterprise: MNDGV-M6PKV-DV4DR-CYY8X-2YRXH OR
FHQNR-XYXYC-8PMHT-TV4PH-DRQ3H
