What is the PCB file format?
.pcb (Printed Circuit Board) is a file format used for storing printed circuit board designs. A .pcb file contains board layout data - copper layers, component footprints, board outline and routing traces - saved in either binary or ASCII text depending on which EDA tool created it.
Because several unrelated applications share the .pcb extension (legacy Altium/Protel, Mentor Graphics PADS Layout and the gEDA pcb tool each write their own incompatible structure), there is no single standard format. Always identify the source program before attempting to open or convert the file. Newer Altium Designer projects use .PcbDoc instead; manufacturing output is exported separately as .GBR Gerber plots.
Uses of .pcb files
Information stored in .pcb files is used for mapping the layout of the physical board to be manufactured - where components sit, how copper traces route between pads, and which areas must remain clear. Without an accurate PCB layout file, circuits on the board would not function properly. Printed circuit boards appear in virtually every electronic device, for example smartphones, and form the basis of connecting mechanical and electrical components with conductive tracks etched into layers of substrate.
Security & safety
RISK: LOWA .pcb layout file is passive design data (geometry, nets, metadata), not executable code, so opening one in a legitimate EDA tool is safe. The real risks are practical: (1) the file may be unopenable without the exact (often paid or discontinued) software that made it, so verify the source program first; (2) avoid 'universal .pcb viewer/converter' downloads from ad portals - they're typically PUP/adware and cannot actually parse proprietary EDA formats; use KiCad, the vendor's tool, or ask for Gerber/PDF exports instead.
Format details
in a nutshell- gnuPaint / GTKWave-era and gEDA PCB layouts - The open-source gEDA 'pcb' designer also uses a .pcb extension, in its own plain-text format.
- ArcSoft PhotoStudio brush / PowerDirector cache - A few non-EDA apps have historically written unrelated .pcb files; very rare today.
Programs that open PCB files
Windows4 apps
Altium Designer
Paid Opens legacy Protel/Altium .pcb and imports P-CAD .pcb; the native tool for Altium-family files. Free 'Altium 365 Viewer' (web) can also view some. 
KiCad
Open-source Free EDA suite; use File > Import to bring in some legacy Altium/EAGLE board designs. Cannot open every proprietary .pcb, but the best free starting point.
Gerber viewer (e.g. gerbv / online viewers)
Open-source Not for the .pcb directly - but the standard way to VIEW a board is to have it exported to Gerber (.gbr) and open that. gerbv is the free reference Gerber viewer. 
macOS1 app
KiCad
Open-source Free cross-platform EDA; import supported legacy board designs, or work in KiCad's own format. 
Linux2 apps
gerbv (gEDA)
Open-source View Gerber output of a board; also relevant if the .pcb is a gEDA 'pcb' text file (open in the gEDA pcb tool). Technical details
deep spec| File purpose | Stores a complete PCB layout: board outline, copper layers, component footprints, trace routing, vias and drill holes |
| Encoding | Binary or ASCII text - format depends entirely on which EDA tool created the file; no universal structure |
| Magic bytes | None; no common file signature exists because multiple incompatible tools use the same .pcb extension |
| Primary creators | Legacy Altium/Protel (binary), Mentor Graphics PADS Layout (binary), gEDA pcb tool (ASCII text) |
| MIME type | application/octet-stream (no registered MIME type for PCB layout files) |
| Layer model | Supports multiple copper layers (top, bottom, inner planes) plus silkscreen, solder mask and paste layers |
| Component data | Stores footprint geometry, reference designators, placement coordinates and rotation angle for each component |
| Copper routing | Encodes trace widths, net assignments, differential pair rules and filled copper polygon pours |
| Drill information | Embeds through-hole and blind/buried via drill sizes and positions within the layout data |
| Design rules | Contains board-level clearance rules, minimum trace width and via/hole size constraints |
| Successor formats | Altium Designer migrated to .PcbDoc; KiCad uses .kicad_pcb (S-expression ASCII); both supersede legacy .pcb |
| Manufacturing output | PCB layout is exported to Gerber (.gbr) plots and drill files (.drl / .xln) for board fabrication |
| Schematic link | Paired with a schematic file (.sch or equivalent) that provides the netlist driving the layout |
| 3D integration | Modern tools embed or link 3D component models within the PCB file for mechanical clearance verification |
| Released | 1980s-1990s (Protel/Tango DOS era and P-CAD) |
PCB conversions
Community Q&A
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