| SpyProof! Encrypted Symmetric Key Format | |
| Synology | |
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Files with the .SPK extension are TAR archives containing an application installation pack, unique to the DiskStation Manager operating system and NAS workstations. After undergoing installation using the Pack Manager, the apps and programs it contains can expand the basic DSM functionality.
The DSM system was developed by Synoloy, the manufacturer of NAS devices. Installing additional software using SPK packs is possible since system version 722.
| .aawdef | Ad-Aware Definitions Format |
| .abr | Adobe Photoshop Brush Format |
| .ac$ | AutoCAD Undo Info Format |
| .acc | DR DOS - ViewMax Format |
| .acl | Microsoft Office Automatic Correction List |
| .acs | Microsoft Agent Character Structured Storage Format |
| .ad | After Dark Screen Saver Format |
| .add | Microsoft Dynamics AX Developer Documentation Format |