PDF files require the free Acrobat Reader. Most were prepared by scanning the original printed versions, and are processed to contain searchable text, using optical character recognition (OCR). The OCR process gets most words right, but there will be some errors, especially in older issues printed on dot matrix printers (e.g., Psorothamnus might be misread as Psomthamnvs). Because of their size, PDF files take longer to download than HTML files.
HTML files present just text, without the original page formatting, and usually without certain highly formatted parts, like the membership application. They download faster because of their smaller size, and are easy to search. When preparing HTML versions from PDF versions, an attempt is usually made to correct any OCR errors.
Searching:
To search the entire archive, go to Google's Advanced Search, and, in the Domain blank, put in http://bristleconecnps.org/Newsletters/ , enter your search terms, and click on Google Search.
At the end of 1994, Vince Yoder produced a comprehensive Index to the content of all issues published to that time. It's in PDF format in this archive.