There are three TurboCAD two DoubleCAD file formats, TCW2CD, TCT, and TCX, 2CT that you can use for saving vector graphics from within TurboCADDoubleCAD.
*TC
W:* (TurboCAD for Windows) - a file format for saving vector graphics from within TurboCAD.
*TC
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Note: If you need to save a drawing that is to be opened by an earlier version of TurboCADDoubleCAD, you can use Save As and save to one version back i.e. In TurboCAD 15 You DoubleCAD 4 You can save as TurboCAD 14as DoubleCAD 3.
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TCW, TCT Import Setup
*Re
store render view:* Opens the drawing in render mode. The file must have been saved in render mode.
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TCW, TCT Export Setup 
*Compression:* Saves the file in the
TCT 2CT compressed format. If the speed of operation is more important than the file size, leave this option disabled.
*Full Precision: TurboCAD * DoubleCAD stores your objects with the maximum possible accuracy.
Full Precision enables the maximum depth of mathematical calculations performed to generate and save entities. When disabled, entities will be calculated and saved using only to four decimal points of precision. This results in faster execution and smaller files, but may compromise accuracy.
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Note: Less than full accuracy can affect the ability of the program to correctly display and edit objects at extremely small scales. Unless you are using a slow machine, and know you do not need extreme accuracy, you should leave Full Precision on.
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Save proxy objects: saves ACIS solid and a number of other TurboCAD Pro object with proxies so that TurboCAD Deluxe or Designer can open the file and see representations of objects that are not supported by those applications. Proxies increase the size of the file, but do allow file to open more quickly.