In case your paragraphs are made by means of Enter, you can re-import the data and add HTML tags to separate paragraphs on a fly right in the process of import without manual adding them.
It is possible with import using Store Manager for Magento application.
Basically the process is the following:
- you do database backup (the usual procedure before mass changes),
-next re-import your products via Store Manager for Magento and during import use the following expression formula -
In expression we used <br> to separate paragraphs instead of <p>, since double <p> for separation can mess up the data, so <br> is more suitable.
Also, please, note in case your line breakers are make by some other method than Enter, please, let us know, so we could adjust the expression for you.
Here is free 2-weeks version of Store Manager for Magento -
so you can give it a try.
Let me know if any assistance required.