It will depend on the nature of the business and if your company is regulated or non-regulated. Assuming you are selling your shares a stock purchase agreement would be the document by means of which you would sell the entire business (company including assets and liabilities), including some other additional documents.
You have been advised really well by Mary and Eric. I willtake a different point of view. I would encourage you to carefully consider why you are selling your business in the first place. I realize that there are a multitude of reasons to do so. I also know that there are many reasons not to sell a business.
The question you need to ask yourself is why. If the business is not doing well, then you will have a very difficult time realizing any significant value from the sale. Why? Because there are more buyers than sellers. The buyers are being advised by their advisors to pass on any business purchase unless the business is very successful and well documented. Potential buyers would rather pay a premium for something good. They also are being advised to not pay a discount on an average performer. Unless there is some unique intrinsic value, it is a difficult sale.
Now on the positive side, let's say you have a successful business and there are buyers that are willing to pay a premium. That said, I would ask you to consider what rate of return and income you are earning from the business. If it's a really good business that is worth a premium, then chances are you are earning an income that you could not earn from investments outside of your business. If you invest outside of your business , for ex. stock market. You give up control and you are subjected to forces that can effect losses that you could not make up for years if ever. Secondly, by owning your business you can carefully invest in qualified plans that will offer tax deferral benefits as well as some form of protections.
Today's economic environment offers lot's of incentives for business owners that are in the right businesses at the right time. I would be happy to speak more to this if you would share more details.
To parrot a bit of what Mary-Alice said above, the various documents needed will vary depending on both the business itself and the structure of the transaction.
In addition to the considerations and documents mentioned above, your sale may require numerous other documents and certificates as schedules and exhibits to accompany the primary documents such as the Asset Purchase Agreement, Stock Purchase Agreement etc. When selling a regulated business, there will likely be specific forms and filings required by the regulator.
If your transaction involves financing of any kind from a financial institution, be prepared to provide due diligence documentation. In a number of instances, a business seller may choose to finance the deal themselves (i.e. take a mortgage and note from the purchaser allowing the purchaser to pay over time). In an instance like that, you will also need a Promissory Note, a Mortgage, and should also secure personal guarantees from the borrower.
It depends on how you are structuring your sale. If it is an asset sale, you will have an Asset Purchase Agreement. A stock sale will require a Stock Purchase Agreement and a merger will have a Merger Agreement. These documents are the primary operative document to effectuate the sale. There are ancillary documents that are required too, such as corporate actions/resolutions, possibly an escrow agreement (if funds are being withheld) and stockholders agreement (depending on post-sale ownership). See the following business sale checklist for a good overview of the prep to closing of a business sale - http://www.mosaichub.com/resource_center/resource/selling-your-business-a-checklist-to-get-you-throu.