For Oracle BI 12c custom content such as images or pdf help files needs to be placed in the following directory:
where /../ is a dynamic folder name such as v-PLM12aFeu7Y.
Within a Report or Dashboard this path may be referenced using the following syntax:
fmap:foldername/file_name (if a subfolder “foldername” was created below /res on filesystem)
the below links provide further information on using fmap or placing custom resources within Oracle BI:
Storing Custom Files Locally and Using the fmap Function to Reference Them
How to configure static content in OBIEE 12c