Bash move and rename by parsing the output of find

I have nested directories of pdf files and I would like to extract them to a higher level directory renaming them as follows:

My files are something like:

./path1/pathA/fileI.pdf

./path1/pathB/fileII.pdf

I want to achieve:

./path1_pathA_fileI.pdf

./path1_pathB_fileII.pdf

I know I can make a list of the files by doing

find . -type f -name "*.pdf"

And I can imagine a solution using

find . -type f -name "*.pdf" | mv -t ...

But I don't know how to fill in the ... because I don't understand parsing and variable assignment in bash. How does one split the path at the '/' and form a new path and file name as above?

Many thanks in advance!

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