Intuit - QuickBooks
Portable Company File
All modern versions of QuickBooks (since 2006) allow you to create a highly-compressed copy of the QuickBooks file called a Portable Company File. This was designed to allow to easily transfer the portable company file electronically, and in many cases even as an email attachment. (Tip: Email is not the safest way to transfer sensitive financial data. It would be best to use a secure file transfer system.) Though the compression level varies from file to file, a Portable Company File may be as small as 10% of the size of your .QBW file.
Shortly after Intuit introduced the QuickBooks Portable Company File, ProAdvisors began to discover that the file has a beneficial alternative use. As a form of file compression, the Portable Company File has all of the indexing removed. If you aren’t familiar with indexing, suffice to say that this part of the QuickBooks database increases file size significantly. When you remove the indexing and then re-index the file (as occurs when you create a Portable Company File and then restore that Portable Company File), you make the indexing of the file more efficient. As a result, a re-indexed file can be significantly smaller, more stable and faster. You will see the most dramatic results from this process when you re-index a file with multiple years of data for the first time.
Though this re-indexing seems very invasive on the file, the process is very stable. Still, you may prefer to create a backup of your data before you overwrite your QuickBooks file by opening a Portable Company File.
(Note from the Editor - even though this use of the QuickBooks Portable Company File has been around for many years, I frequently see new ProAdvisors amazed by the fact that this is one of many resources for dealing with large files, slow performing files, and some forms of data damage. As such it is a good practice to keep this 'valuable tip' in the minds of QuickBooks users and professionals alike. )