The file-type library

What each extension really is, how to open it, and whether it deserves caution — with the file identifier for anything the name doesn't explain.

Diagnostics & crash files

.dmp
Windows Memory Dump .mdmp
Application Minidump .wer
Windows Error Report .evtx
Windows Event Log .reg
Registry Script .etl
Event Trace Log .cer
Certificate File .crt
Certificate File .pem
PEM Container .der
DER-Encoded Certificate .pfx
PKCS#12 Bundle .p12
PKCS#12 Bundle .csr
Certificate Signing Request .key
Private Key File

Windows system files

.dat
Registry Hive / Generic Data .pf
Windows Prefetch File .lnk
Windows Shortcut .tmp
Temporary File .inf
Setup Information File

Programs & executables

.sys
Windows Kernel Driver .dll
Dynamic-Link Library .exe
Windows Executable .msi
Windows Installer Package .scr
Windows Screensaver .jar
Java Archive

Scripts

.bat
Batch Script .cmd
Command Script .ps1
PowerShell Script .vbs
VBScript File .js
JavaScript File

Data & configuration

.ini
Configuration File .log
Log File .xml
XML Document .json
JSON Document .csv
Comma-Separated Values .txt
Plain Text File .torrent
Torrent Metadata

Archives & images (disc)

.zip
ZIP Archive .7z
7-Zip Archive .rar
RAR Archive .iso
Disc Image .cab
Windows Cabinet Archive

Documents

.docx
Word Document .xlsx
Excel Workbook .pdf
PDF Document

Images

.jpg
JPEG Image .png
PNG Image .ico
Windows Icon .heic
HEIC Image

Media