Use the PDF Search plugin if you want your PDF files to be searchable within Omeka.
This plugin enables searching on PDF files by extracting their texts and saving them to their parent items. This normally happens automatically, but there are times when you'll want to extract text from all PDF files that exist in your Omeka archive; for example, when first installing the plugin and when items are being created by other plugins. You can run the bulk text extraction process in the plugin's configuration page. The process may take some time to complete.
Your server must have an up-to-date pdftotext command-line utility installed for the plugin to function. If you get an error message while attempting to install the plugin, you don't have the required utility. Speak with your server administrator about installing pdftotext. Older versions of pdftotext may result in garbled or incomplete text during extraction, particularly when the PDF contains Unicode characters. Make sure your server is using the pdftotext that's available in poppler-utils, not the outdated Xpdf version.