AutoCAD is normally not supplied with the user-defined startup file acad.lsp; you create (Notepad can be used) and maintain the file yourself. You can create an acad.lsp file if you regularly use specific AutoLISP routines. When you start AutoCAD, it searches the support file search path for an acad.lsp file. If an acad.lsp file is found, it is loaded into memory.
The acad.lsp file is loaded at each drawing session startup when AutoCAD is launched. Because the acad.lsp file is intended to be used for application-specific startup routines, all functions and variables defined in an acad.lsp file are only available in the first drawing. You will probably want to move routines that should be available in all documents from your acad.lsp file into the acaddoc.lsp file.
The recommended functionality of acad.lsp and acaddoc.lsp can be overridden with the ACADLSPASDOC system variable. If the ACADLSPASDOC system variable is set to 0 (the default setting), the acad.lsp file is loaded just once: upon application startup. If ACADLSPASDOC is set to 1, the acad.lsp file is reloaded with each new drawing.
ACADLSPASDOC is ignored in SDI (single document interface) mode. When the SDI system variable is set to 1, LISPINIT controls the reinitialization of AutoLISP between drawings. When LISPINIT is set to 1, AutoLISP functions and variables are valid in the current drawing only; each time you start a new drawing or open an existing one, all functions and variables are cleared from memory and acad.lsp is reloaded. Changing the value of LISPINIT when SDI is set to 0 has no effect.
The acad.lsp file can contain AutoLISP code for one or more routines, or just a series of load function calls. The latter method is preferable, because modification is easier. If you save the following code as an acad.lsp file, the files mysessionapp1.lsp, databasesynch.lsp, and drawingmanager.lsp are loaded every time you start AutoCAD.
Warning! Do not modify the reserved startup file acadYEAR.lsp (acad2000.lsp, acad2000i.lsp acad2002.lsp, acad2004.lsp, acad2005.lsp, acad2006.lsp, acad2007.lsp, acad2008.lsp, acad2009.lsp, acad2010.lsp, acad2011.lsp, acad2012.lsp, acad2013.lsp, acad2014.lsp, acad2015.lsp). Autodesk provides this file, which contains AutoLISP defined functions that are required by AutoCAD. This file is loaded into memory immediately before the acad.lsp file is loaded.
Do not modify the reserved file acadYEAR.lsp; it contains AutoLISP-defined functions required by AutoCAD. The file acadYEAR.lsp is loaded into memory immediately before acad.lsp.
How to create acad.lsp if it does not exist
In the folder where you want to save acad.lsp right click and select New>Text Document. Change the name to acad.lsp. Now you should be able to double click on the file and typically edit it in Notepad.
Or start Notepad, edit, save, ready.
Examples on location for acad.lsp
C:\Program Files\AutoCAD 2008\Support
C:\Documents and Settings\<loginname>\Application Data\Autodesk\AutoCAD 2008\R17.1\enu\Support
or in Windows Vista
If you want to find folders that are searched by AutoCAD run the OPTIONS command and look at the Files tab and at the Support File Search Path.
Load order of files in AutoCAD
Files in acad.rx
Partials to Main CUI/CUIX named MNLs
Partials to Main CUI/CUIXloaded LSPs and MNLs in the order seen in CUI
Main CUI/CUIX named MNL
Main CUI/CUIX loaded LSP and MNL in the order seen in CUI
Partials to Enterprise CUI/CUIX named MNLs
Partials to Enterprise CUI/CUIX loaded LSPs and MNLs in the order seen in CUI
Enterprise CUI/CUIX named MNL
Enterprise CUI/CUIX loaded LSP and MNL in the order seen in CUI
Express Tools loaded LSP and MNL in the order seen in CUI
Files in the startup suite in listed order seen in APPLOAD
Script file started by acad.exe command line switch /b
This applies to AutoCAD 2000, AutoCAD 2000i, AutoCAD 2002, AutoCAD 2004, AutoCAD 2005, AutoCAD 2006, AutoCAD 2007, AutoCAD 2008, AutoCAD 2009, AutoCAD 2010, AutoCAD 2011, AutoCAD 2012, AutoCAD 2013, AutoCAD 2014, AutoCAD 2015
Update related to AutoCAD 2013 SP1: AutoLISP and VBA Security Controls in AutoCAD 2013 SP1. New /nolisp Startup Switch. LISPENABLED, AUTOLOAD, AUTOLOADPATH system variable added.
The acad2013.lsp and acad2013doc.lsp files will now be loaded only from their default installation folders: