To upload a document:

1. Click New Document from the Documents tab or click New next to Recent Documents on the documents home page. If you do not have a New Document option, check if you have the correct permissions.
2. Specify a descriptive Document Name. If you want to use the file name, leave this field blank. The file name will appear automatically when you upload the file.
3. If you have the “Customize Application” permission, enter a unique name to be used by the API and managed packages.
4. You can check:
5. Internal Use Only if the document is confidential. Checking this box does not change the visibility of the file but prevents it from being publicly accessible.
6. Externally Available Image if the document is an image, such as a logo, that's not confidential. Check this box to:
7. Make the image available from HTML email templates without requiring a Salesforce username and password
8. Use the image as a custom tab icon or custom app logo, which do require a Salesforce username and password to view
9. Display the image in meeting requests
10. Select a folder for the document.
11. Enter a description to use later as search criteria.
12. Enter keywords that you can use later as search criteria.
13. Select a document or path option.
14. To upload a document, click Browse, choose the file, and click Open.
15. To store a link to the document, enter the location of the document. Enter a path and file name or a URL such as: C:\Quotes\quote.doc, \\Server\Departments\Marketing\logo.doc, or http://www.salesforce.com.
16. Click Save.

To replace a document with an updated version:

1. Display the document you want to replace. For instructions on locating a document in the document library, see Searching for Documents.
2. Click Replace Document.
3. Select a document or path option.
4. To upload a replacement, click Browse, choose the file, and click Open.
5. To store a link to the replacement, enter the location of the replacement. Enter a path and file name or a URL such as: C:\Quotes\quote.doc, \\Server\Departments\Marketing\logo.doc, or http://www.salesforce.com.
6. Click Replace Document.    

• Documents stored as links cannot be attached to emails, but they save space in your document library.
• If document content search is enabled, Salesforce will also perform a full-text search of the document. When a new document is uploaded or an old one is replaced, its contents are available for searches. For more information, see Searching for Documents.
• Salesforce stores the most recent upload date as the modified date.
• You can upload documents that have file names of up to 255 characters including the extension.
• The size limit for any document you upload is 5 MB. The maximum size for a custom-app logo is 20 KB.
• Your organization’s used file storage includes all files stored in the document library.
• If the Disallow HTML documents and attachments security setting is enabled for your organization, you cannot upload files with the following file extensions: .htm, .html, .htt, .htx, .mhtm, .mhtml, .shtm, .shtml, .acgi.