Here's a small trick to convert your documents to the PDF format, without using any conversion software.
First you will need to make sure that the application you are using to view your files or documents doesn't possess a built-in feature to save your files in PDF format. Click on the File menu and if the Export to PDF or Export as PDF options are available, then you won't need this tip.
Converting documents to PDF using the virtual printer of Mac OS X
First select the document you want to convert. You can choose a file created with LibreOffice or Microsoft Office, a web page from your browser, a picture opened with Preview or documents from any other application.
Open the document, image or file using its default software. Then click on File > Print.
In the menu that opens, select Save as PDF. Rename the file if needed, but make sure that you save the file using the .pdf extension.