Why use PDF files
Firstly and most importantly your PDF documents will look the same on all hardware, software and operating systems. Nearly all operating systems nowadays come with a PDF reader, and if not, free readers are easily downloadable from the internet. PDF files help to get your documents across clearly and avoid any communication problems.
Lets take an example. Say your working on an older computer using an older version of Word, or even a different word processor (say Libre Office). If you now send a copy of your document in Word format to someone with a newer version of Word, then the chances are that it won't display exactly as it does on your word processing software. Take the same scenario, and print the document to a PDF file. The person on the other computer will now see your document exactly as you created it.
Take it one step further. You are now creating a document from a number of different software applications. This is quite common in business. So you may have a number of separate documents from different applications, that define just one document. Giving the application to a client in pieces is somewhat messy and looks unprofessional. Here PDF files once again can help, many freeware applications, including Trekker , can be used to combine the documents into one document.
Embedding you say! Yes you can use embedding between certain applications, and this is often very useful when available. However, when embedding is supported your document will start to become very large. And once again using the PDF format to transmit a document helps. For a start the PDF file does not need all of the extra information needed by the creating application, it only needs the information sufficient to display the document correctly, it doesn't need the information to let it know how the document was created. On top of that the compression used by PDF files is substantial, meaning an even further reduction in file size.
Which leads on to the point of when not to use a PDF file. In the case when work is being carried out by a number of parties, and before the finished product, it will usually be best to use the original software application file. For example, if you send your co-worker a PDF file of a Word document that he is then supposed to also edit, he would first have to change the PDF file back into Word document first, so in this case it would be much better to send the original Word document.
PDF files can also be useful to document changes over time. Instead of printing a paper copy to archive. You can make a PDF version of the document and include a date stamp in the filename. This way you can have a record of the changes to a document over time. Please note that when you use a computer media to store important documents, you should make sure that backups of the data are created on a different media.