If you use this type of content on your site without making any changes to it, will it negatively affect your rankings/
If you have nothing but duplicate content then don't expect any organic traffic at all. You should rewrite these PLR articles in order to make them unique. Use Copyscape when in doubt
There are several factors involved here. If your pages are optimized, if your site has a good structure, if you manage to get backlinks, if you update your site regularly and if you have quality content, then I would not worry too much about duplicate content even if you post PLR material to your site. The thing to avoid is duplicate content inside your own site. Duplicate content is a never ending debate. Focus on quality and you will do well in the long run.