When rendering PDFs, Gravity PDF sets a
DONOTCACHEPAGE constant that is suppose to prevent any caching plugin from running when we display the PDFs. We tested all popular caching plugins with Gravity PDF and out of the box there were no issues. However, there are edge cases that can cause caching plugins to try apply cache techniques to the PDF anyway. When that happens you may see weird characters on the screen instead of your PDF document (for those technically savvy, we narrowed this down to a Gzip Compression issue).
To test if there is a conflict between Gravity PDF and your caching plugin just temporarily deactivate the caching plugin and see if the problem with the PDF persists. If the PDF starts displaying correctly you've found the conflict. If your caching plugin allows you to manually prevent caching on certain URLs it's very easy to resolve. Just exclude
/pdf/ from being cached and retest.