PDF File Links : Relative and Absolute Paths
File Links in PDF Documents - Relative vs Absolute
PDF documents are often designed to contain links to other documents or files. Typically, there is a group of cross-linked documents that needs to be burned on CD/DVD or published on a website.  PDF bookmarks and links can point to external files using a variety of "actions" (such as "Open a file" or "Go to a page view in another document").  These actions can refer to external files by using either relative or absolute file paths. A full path or absolute path is a path that points to the same location on one file system regardless of the working directory of the document that contains a link. It is usually written in reference to a root directory. A relative path is a path relative to the current document's directory. If a document uses absolute paths then it cannot be moved to another computer (unless this computer contains exactly the same folder structure) or written on CD without breaking the links.
Absolute File Paths Explained
Generally, you do not want to have any absolute file references in your PDF files. All links and bookmarks that use absolute file references will not work if documents are moved into a different location. However, Adobe Acrobat does not provide you any way of checking if a particular file link is using an absolute path or let you to choose what type of a file path to use. Acrobat always shows all file paths as fully resolved (relatively to a current location of the document) and they will always appear in Acrobat user interface as full paths. Sometimes, this makes some users to worry that their files contain absolute file links. Actually, Acrobat always tries to create only relative file paths when a user is adding any action that refers to an external file. However, it is not always technically possible to create a relative path. For example, if two documents are located on different disk drives, then it is not possible to create a relative path from one file to another. Always place all documents that refer to each other on the same disk drive to avoid accidentally introducing of absolute file paths. Never add links to a temporary PDF document - always save it to a known location first (temporary document is a document that has been created by Adobe Acrobat and has not been yet saved, typically it has "Untitled" document name). Temporary document are automatically created by Adobe Acrobat in a special folder that may be located on a different disk drive than files you are linking to. Another source of the absolute paths are many legacy third-party applications that may produce documents with absolute file paths.    
Finding and Fixing Absolute File Links
The AutoBookmark plug-in offers a variety of tools for detecting and even automatically fixing (converting them into relative form) absolute file references. You can use link reporting tool ("Plug-ins > Link > Create Link Report" menu) to quickly generate a detailed report listing all external file references and detecting any absolute paths in link annotations. Use "Cleanup links and bookmarks" feature to automatically convert any absolute file paths into relative ones. This valuable tool saves a lot of time and trouble by detecting and fixing all links and bookmarks that use absolute paths making your PDF documents ready to be published on a website or burned on CD. These are just a few examples of the numerous handy functions that AutoBookmark plug-in can offer. Visit AutoBookmark web page for the detailed information about software features.