The DoubleCAD library is where you can access symbols and parts. Symbols and parts, like blocks and groups, are objects available for repeated use. But while groups and blocks are internal to a drawing, library items are external files. Generally, each symbol or part is stored as a file, and libraries of files are stored in specified library folders. Any Windows folder can be recognized as a library folder, and any vector drawing file (not just DoubleCAD files) can be used as a symbol.
A symbol or part is placed into a drawing as a group; it has a unique name and is selected and manipulated as a single object. Because they are placed as groups, each instance of a part or symbol creates additional drawing data, and inserting numerous library items can increase your drawing size significantly. If you need to use many instances of a particular symbol or part, you can reduce your file size by making it into a block. A block is stored internally in a drawing, and references to it are inserted into the drawing rather than the objects themselves. See Blocks.DoubleCAD
provides several symbols and parts, organized in folders by category. Each symbol is a separate *.2cd file, and parts are *.ppm files. These files are installed, by default, to the "Symbols" folder in the DoubleCAD installation folder.
You can modify these symbols (though it is preferable to modify copies and leave the originals intact), and also create and save your own symbols.
Symbol manipulation is done via the Library Palette.