It is not possible with just FileMaker, you'd also need to find and add a plug in. You can use container fields to store copies of or references to the PDF's but file maker cannot search the content of the PDF files in order to find the correct record with the PDF that contains that text. I have heard of a plug in, however, that can import the text contents of the PDF into a text field so you could have the PDF inserted into a container field and a copy of it's contents inserted into a text field that then can be searched. (I do not recall the name of the plug in developer nor their plug in, so you'd have to do some web searching to find them.)
Note that some PDF's display text but are a PDF of an image of that text and this would not be data that even this plug in could import into a text field. In such cases you can't even open the PDF and use Adobe reader to search the pages of the PDF for text.