Melissa .. no it isn't, an online converter will only be any good if you can get online .. and you are giving your document to someone else.
(online converters should be a last resort)
How hard can it be to (in ANY application that can print) to select
File > Print
Click on Print to File
Output format: tick the PDF box
then click the Print button
You'll then find the PDF in your home folder.
It's EXACTLY like printing the document .. but instead of being sent to your printer, a PDF file is created instead.
But there's something wrong if you can't export to PDF from within LibreOffice .. it certainly works on my system.