PageSpeed will rewrite links to PDFs to include a content-hash. PDFs are identified by having extension ".pdf". Note that this requires a background asynchronous fetch of the PDF; therefore the page may not be rewritten the first time. If it isn't, wait a few seconds and reload.

• Standard link to a pdf, will be cache extended: example.pdf
• Embedded pdf, will also be cache extended:
  
• Link to a PDF with extension ".notpdf". It won't be cache extended because a ".pdf" extension is required: example.notpdf
• Link to a PDF with a query parameter, will be cache extended: example.pdf?a=b