There is a customer of ours that always sends multiple PDF files for reference, together with .itd files to translate.
Since the PDFs illustrate the mechanical maintenance procedures described in the translation files, being able to search the PDFs to find the correct illustrations is essential. Searching each of them separately would be time consuming (and tedious).
Fortunately, there is an easy way to search numerous PDFs all at the same time.
Using Foxit Reader (an excellent free tool, much superior to the bloated Adobe Reader), just hit Ctrl+Shift+F to open the search pane,
select the All PDF documents in radio button, browse for the folder where you have saved your reference PDFs, select the appropriate checkboxes, and hit Enter.
Foxit Reader will display all the files (and location in the files) where your search terms are to be found.