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Re: ACAD Protection

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The "turn a DWG file into a PLT file" method of drawing protection is useful to know about, but it's device-dependent (i.e., the recipient needs to have an output device that's capable of accepting the plot file) and may not serve the client's needs.

A PLT file is a simplified vector representation of your AutoCAD drawing. The PLT representation contains vectors and instructions for how to show those vectors (line thickness, color, screening, and any other special effects), and that's about it. Layer information is absent. Text is converted to vectors. Drawing structure (blocks, xrefs, etc.) is gone. Essentially it's a plotted representation of your drawing in electronic form.

If the recipient has an output device that understands your PLT file format (often HP-GL/2, the most common HP plotter format), then he can send the plot files to that device and get plotted drawings. If she has a piece of software that reads HP-GL/2 files, she may be able to view the plotted representation on the screen. With such software, she also might be able to convert the PLT to a different format (e.g., DXF) and bring it back into AutoCAD. But the result back in AutoCAD will be a pale shadow of your original DWG file (because of the loss of layers, text strings, drawing structure, etc.). That's why people often advocate sending PLT files as a means of drawing protection.

However, the client who asks for AutoCAD drawings often is interested in doing something more than just plotting. Sometimes that "something more" is legitimate (e.g., electronic coordination, or full electronic submittal to the client). On the other hand, the firm that generates the AutoCAD drawings has a legitimate concern that the drawings not be misused (e.g., relied on uncritically for shop drawings, designs or details stolen...).
In my view, the concerns of all parties involved are best addressed in the contract for design services, not by ex post facto attempts to protect the drawings. Your contract should state exactly what your deliverables are (both hardcopy and electronic) what they're to be used for, and what they *aren't* to be used for.

- Mark Middlebrook