| .XNG | Unknown Developer | Ficheiros de Texto | FishXing Culvert Data File | FishXing | Unknown Developer |
| .XNX | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .XOS | Xaos Tools | Ficheiros de Imagem Raster | Xaos Tools Bitmap Image | Unknown Software | Unknown Developer |
| .XPE | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XPN | Quest Software | Uncommon Files | Quest Saved Explain Plan | Unknown Software | Unknown Developer |
| .XSEND | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .XT* | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .XTE | PerkinElmer | Ficheiros de Dados | LabChip XTe Data | Unknown Software | Unknown Developer |
| .XUP | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XVID-TRL | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .XWF | Nuance | Uncommon Files | OmniPage Workflow File | Unknown Software | Unknown Developer |
| .XWT | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .XXC | CentraLine | Ficheiros de Dados | Centraline COACH Controller Firmware | Unknown Software | Unknown Developer |
| .XXL | Unknown Developer | Ficheiros Compactados | File Archive Handler Compressed Archive | File Archive Handler | Unknown Developer |
| .XXX | BloodDolly | Ficheiros Encriptados | TeslaCrypt 3.0 Ransomware Encrypted File | Unknown Software | Unknown Developer |
| .XXXX | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .XXZ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .XZP | Unknown Developer | Ficheiros de Dados | XZP Container Format | Unknown Software | Unknown Developer |
| .YAD | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .YAR | Unknown Developer | Ficheiros Compactados | YAK Compressed Archive | Unknown Software | Unknown Developer |
| .YBS | Unknown Developer | Ficheiros Compactados | YBS Compressed Archive | YBS | Unknown Developer |
| .YC | Unknown Developer | Ficheiros Compactados | YAC Compressed Archive | Unknown Software | Unknown Developer |
| .YIN | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .YJF | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .YKI | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .YLM | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .YN | Unknown Developer | Ficheiros Compactados | Audio Utility Tuningwrench Compressed File | Unknown Software | Unknown Developer |
| .YNM | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .YNX | Unknown Developer | Ficheiros de Áudio | Segmax Seqprest Compressed File | Unknown Software | Unknown Developer |
| .YRA | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .YTS | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .YUF | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .YYC | Unknown Developer | Ficheiros de Dados | Wave Sapphire Distribution File | Unknown Software | Unknown Developer |
| .YZF | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ZAE | Unknown Developer | Ficheiros de Dados | ZAwinEHE Project | Unknown Software | Unknown Developer |
| .ZAL | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZAX | Zaxcom | Ficheiros de Áudio | Zaxcom Audio Data | Unknown Software | Unknown Developer |
| .ZBJ | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZBS | Unknown Developer | Ficheiros de Dados | Super-K Data | Super-K | Unknown Developer |
| .ZBX | Unknown Developer | Uncommon Files | Disk Volume Identification | Unknown Software | Unknown Developer |
| .ZCH | Unknown Developer | Uncommon Files | ZIG Game Construction Kit Data | Unknown Software | Unknown Developer |
| .ZDB | Synacor Inc. | Ficheiros de Dados | Zimbra Database File | Unknown Software | Unknown Developer |
| .ZDE | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZDF | Unknown Developer | Ficheiros de Dados | Zone Definition File | Unknown Software | Unknown Developer |
| .ZDI | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZEB | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ZET | Unknown Developer | Ficheiros Compactados | ZET Compressed Archive | Unknown Software | Unknown Developer |
| .ZFSENDTOTA | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ZGEPROJ | Unknown Developer | Ficheiros de Jogo | ZGame Editor Project File | ZGameEditor | Unknown Developer |
| .ZGZ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ZH3 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ZIQ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ZONE | Apple | Ficheiros de Dados | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .ZPAR | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ZPKG | Zyxel Communications | Ficheiros Executáveis | Zyxel NSA-32x Application Package | Unknown Software | Unknown Developer |
| .ZR4 | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZUC | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ZUN | Unknown Developer | Uncommon Files | Recogsp File | Unknown Software | Unknown Developer |
| .ZVQ | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZVZ | Unknown Developer | Ficheiros Web | Possible Virus File | Should Not Be Opened Manually | Unknown Developer |
| .ZX | Unknown Developer | Ficheiros de Jogo | KGB ZX Spectrum Emulator Snapshot | KGB | Unknown Developer |
| .ZXF | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .ZXL | Unknown Developer | Ficheiros de Dados | Immersioni Dive Logbook DL7 | Immersioni Dive Logbook DL7 | Unknown Developer |
| .Z•À_•À_P | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| ._CRYPT | WhatsApp Inc | Ficheiros Codificados | Virus.Win32.Gpcode.ak | Unknown Software | Unknown Developer |
| .~AN | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
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