I create PDF files from my Adobe Illustrator files by saving as. I would prefer it to create the pdf file and retain the AI file but sometimes it converts the ai file to a pdf. Not all the time, only sometimes. Why is this? Is there a way to create PDF files without having it convert your current artboard to a PDF file.
When you Save As, it may "replace" your file in Illustrator but your original file will still exist (and you can open it back up). So if your file is AI and you save as PDF the AI file will still exist.
You can always use "Save A Copy..." instead if you prefer to keep the original open while saving the other format.
Here's a recording I did showing the issue and then showing using "Save A Copy..." http://i.imgur.com/242rdFC.gifv