KB: Troubleshooting "File Type Not Recognized" Errors When Opening Protel .pcb Files in Altium Designer
Updated: 九月 07, 2026
Altium Designer
If Altium Designer displays a "File type not recognized" error when opening a .pcb file, the file may not be a legacy Protel PCB document even though it uses the .pcb extension. Many ECAD applications historically used the same extension, making file identification difficult. To determine whether the file is a supported Protel format, inspect the file header in a text editor and compare it against known Protel PCB signatures. If the file is confirmed as a Protel PCB file and still cannot be opened, further analysis of the file may be required.
概览
If Altium Designer displays a "File type not recognized" error when opening a .pcb file, the file may not be a legacy Protel PCB document even though it uses the .pcb extension. Many ECAD applications historically used the same extension, making file identification difficult. To determine whether the file is a supported Protel format, inspect the file header in a text editor and compare it against known Protel PCB signatures. If the file is confirmed as a Protel PCB file and still cannot be opened, further analysis of the file may be required.
Solution Details
Unrecognized Format Error When Opening Files
When opening a
.pcb file in Altium Designer, you may receive a "File type not recognized" error. Although Altium Designer associates the .pcb extension with legacy Protel PCB documents, not every file with this extension was created by Protel.Legacy ECAD Tools Shared The Same Extension
Many PCB design tools adopted the
.pcb extension during the DOS era when file extensions were limited to three characters. As a result, files from different ECAD applications can share the same extension while using entirely different file formats. While Protel used the .pcb extension and Altium Designer continues to recognize it as a Protel PCB document, the file may actually belong to another PCB design system.Determine Whether The File Is A Protel PCB
- Inspect the file contents to identify the actual file format.
- Compare the file header against known Protel PCB file signatures.
- If the file header does not match a Protel PCB format, identify the originating ECAD application and use the appropriate import method.
- If the file header matches a Protel PCB format but still cannot be opened, the file may be corrupted or require additional investigation.
Inspect The File Header And Verify Support
- Open the
.pcbfile in a text editor such as Notepad or Notepad++, even if the file appears to be binary. - Review the beginning of the file and identify the file header.
- Compare the header against the known Protel PCB signatures shown below.
- In Altium Designer, navigate to Tools » Preferences » File Types and verify that the
.pcbextension is associated with Protel PCB Documents. - If the file header does not match a Protel PCB format, identify the originating ECAD application and use the corresponding import method.
- If the file header matches a Protel PCB format and Altium Designer still reports "File type not recognized," collect the file for further analysis.
Protel PCB File Headers
| Format | Expected File Header |
|---|---|
| Protel PCB 2.8 ASCII (*.pcb) | PCB FILE 6 VERSION 2.80 |
| PCB 3.0 Binary File (*.pcb) | PCB 3.0 Binary ... |KIND=Protel_Advanced_PCB|VERSION=3.00|... |
| PCB 4.0 Binary File (*.pcb) | PCB 4.0 Binary ... |KIND=Protel_Advanced_PCB|VERSION=3.00|... |
Finding one of the file headers listed above is a quick way to confirm that a .pcb file originated from a supported Protel PCB format. If none of these signatures are present, the file was likely created by another ECAD application that also uses the .pcb extension.