What is .SchDoc? Altium Schematic File Explained

If you’ve downloaded reference designs from semiconductor vendors, received design files from contractors, or inherited projects from other engineers, you’ve likely encountered .SchDoc files. This is Altium Designer’s native schematic document format—the file that captures your circuit’s logical design before it becomes a physical PCB.

Understanding the .SchDoc format matters whether you’re an Altium user managing projects, a KiCad user trying to import legacy designs, or someone evaluating design files from suppliers. This guide explains what .SchDoc files contain, how they’re structured, and your options for opening, converting, and working with them.

What is a .SchDoc File?

A .SchDoc file is a schematic document created by Altium Designer, the professional PCB design software from Altium Limited. Each .SchDoc file represents one sheet of an electronic circuit schematic, containing component symbols, electrical connections, net labels, power ports, and design parameters.

The .SchDoc format has been Altium’s standard schematic file type since the Protel DXP days (early 2000s), evolving from the older .SCH format used in Protel 99 SE and earlier versions. Despite format updates across Altium releases, the .SchDoc extension has remained consistent, making it immediately recognizable to anyone working with Altium designs.

.SchDoc File Identification

Altium Project File Structure

A .SchDoc file doesn’t exist in isolation—it’s part of an Altium Designer project that includes multiple file types working together.

Essential Altium Project Files

When working with Altium designs, you typically need both the .PrjPcb project file and all associated .SchDoc files to open and compile a complete design. The project file references which schematic sheets belong to the design and defines their hierarchical relationships.

Inside the .SchDoc File Format

The .SchDoc format uses Microsoft’s OLE (Object Linking and Embedding) Compound Document structure—the same container format used by older Microsoft Office files (.doc, .xls). This makes the binary format somewhat accessible to reverse engineering efforts, which has enabled third-party import tools.

.SchDoc Internal Structure

Inside the FileHeader stream, schematic objects are stored as records with pipe-delimited properties. Each record has a RECORD type identifier that determines what kind of object it represents.

Common Record Types in .SchDoc Files

Properties within each record are encoded as name=value pairs, with coordinates stored in units of 1/100 inch (10 mils). This text-based property encoding makes the format relatively straightforward to parse once you extract it from the OLE container.

Binary vs ASCII .SchDoc Files

Altium Designer can save .SchDoc files in two formats: the default binary (OLE Compound Document) format and an ASCII text format. This distinction matters significantly for interoperability.

Format Comparison

Many EDA tools that import Altium files require the ASCII format specifically. If you’re sharing designs with users of EasyEDA, DipTrace, or using conversion tools, saving as ASCII .SchDoc improves compatibility significantly.

How to Save ASCII .SchDoc in Altium Designer

1. Open your schematic in Altium Designer
2. Select File → Save As
3. In the “Save as type” dropdown, choose “Advanced Schematic ASCII (*.SchDoc)”
4. Save the file with your desired name

The resulting file is plain text that you can open in any text editor to inspect the contents—useful for debugging import issues or understanding what changed between versions.

Multi-Sheet and Hierarchical Designs

Complex designs often span multiple .SchDoc files organized in flat or hierarchical structures. Understanding this organization is essential when working with larger Altium projects.

Design Structure Types

In hierarchical designs, a top-level .SchDoc contains sheet symbols that represent lower-level schematic sheets. Each sheet symbol’s filename property points to another .SchDoc file. Sheet entries on the symbol connect to ports on the child sheet, creating the electrical connectivity between hierarchy levels.

Sheet Symbol Properties

When importing hierarchical Altium designs into other tools, you typically need to select the top-level .SchDoc file, and the import process should automatically pull in referenced sub-sheets.

How to Open .SchDoc Files

The primary way to open .SchDoc files is with Altium Designer, but several alternatives exist depending on your needs.

Software That Opens .SchDoc Files

Opening in Altium Designer

Double-click the .SchDoc file if Altium is installed and associated with the file type, or:

1. Launch Altium Designer
2. Open the associated .PrjPcb project file
3. Double-click the schematic in the Projects panel

Opening individual .SchDoc files without their project can work for viewing, but you’ll lose connectivity information and may see warnings about missing libraries.

Viewing Without Altium

Altium offers a free web-based viewer at Altium 365 that can display .SchDoc files without requiring a license. Simply upload your file to view the schematic, though editing capabilities are not available.

For command-line or programmatic access, several open-source projects can parse .SchDoc files:

Converting .SchDoc Files

Converting .SchDoc files to other formats is a common requirement when migrating between EDA tools or collaborating with engineers using different software.

Import Support (From .SchDoc)

Converting to KiCad

KiCad 7 and later versions include native Altium import capability:

1. In KiCad, select File → Import Non-KiCad Project → Altium Project
2. Select the top-level .SchDoc file
3. For hierarchical designs, KiCad automatically imports sub-sheets
4. Map layers as prompted
5. Review and verify the imported design

For older KiCad versions or problem files, the altium2kicad online converter (www2.futureware.at/KiCad) provides an alternative approach, though results may require manual cleanup.

Export from Altium

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Common .SchDoc Issues and Solutions

Working with .SchDoc files from various sources often presents challenges. Here are solutions to common problems.

Troubleshooting Guide

Version Compatibility

.SchDoc files from newer Altium versions may not open correctly in older versions. When sharing designs, confirm the recipient’s Altium version and consider saving in a compatible format. ASCII format tends to be more backward-compatible than binary.

.SchDoc vs Other Schematic Formats

Understanding how .SchDoc compares to other schematic formats helps when evaluating design files or choosing tools.

Schematic Format Comparison

Altium’s .SchDoc format offers good functionality but remains proprietary. For maximum interoperability, save ASCII versions when sharing outside your organization.

Useful Resources for .SchDoc Files

Official Documentation

Conversion Tools

Component Libraries

Frequently Asked Questions About .SchDoc Files

Can I open .SchDoc files without Altium Designer?

Yes, several options exist. Altium 365 Viewer (free, web-based) lets you view .SchDoc files without a license. KiCad 7+ can import .SchDoc files directly through its import wizard. EasyEDA and DipTrace can import ASCII-format .SchDoc files. For programmatic access, open-source parsers like python-altium can extract and convert the contents. However, for full editing capability with guaranteed fidelity, you need Altium Designer or CircuitStudio.

How do I convert .SchDoc to KiCad format?

In KiCad 7 or later, go to File → Import Non-KiCad Project → Altium Project and select your .SchDoc file. KiCad will import the schematic and create native .kicad_sch files. For hierarchical designs, select the top-level schematic and KiCad pulls in sub-sheets automatically. If the direct import fails, try saving the file as ASCII format in Altium first, or use the altium2kicad online converter as an alternative. Always verify the converted design carefully, as some elements may not translate perfectly.

What’s the difference between binary and ASCII .SchDoc files?

Binary .SchDoc files use Microsoft’s OLE Compound Document format—compact but not human-readable. ASCII .SchDoc files store the same information as plain text with pipe-delimited properties. Binary is the default when you save normally in Altium; ASCII requires explicitly choosing “Advanced Schematic ASCII” when saving. ASCII files are larger but work better with version control systems (Git), are easier to debug, and are required by several third-party import tools like EasyEDA.

Why won’t my .SchDoc file import into EasyEDA or DipTrace?

These tools require ASCII-format .SchDoc files, not the default binary format. Open the file in Altium Designer, then use File → Save As and select “Advanced Schematic ASCII (*.SchDoc)” from the format dropdown. Also check for encoding issues—files from older Altium versions may use GBK2312 encoding instead of UTF-8, causing garbled characters. Open the ASCII file in a text editor and resave as UTF-8 if needed.

How do I handle hierarchical designs with multiple .SchDoc files?

Hierarchical Altium designs consist of multiple .SchDoc files linked through sheet symbols. The top-level schematic contains sheet symbols that reference child schematics via their filename properties. When importing into other tools, always start with the top-level .SchDoc file—most importers automatically discover and process the linked sub-sheets. If links are broken (common when files are moved), you’ll need to update the filename references in the sheet symbols to point to the correct paths.

Conclusion

The .SchDoc format has served as Altium Designer’s schematic standard for over two decades, making it one of the most common proprietary schematic formats in professional electronics design. While the binary format isn’t open, the availability of ASCII export and the OLE-based structure have enabled reasonable interoperability through import tools and converters.

Whether you’re working natively in Altium, importing legacy designs into KiCad, or evaluating reference designs from semiconductor vendors, understanding the .SchDoc format helps you work effectively with these files. The key practical takeaway: when sharing .SchDoc files outside your organization or importing into non-Altium tools, always save as ASCII format first. This simple step solves most compatibility issues and makes troubleshooting much easier.

As KiCad and other tools continue improving their Altium import capabilities, working with .SchDoc files becomes increasingly accessible even without an Altium license—though for production work in Altium environments, there’s still no substitute for the native application.