All is setup including pre-reqs. Uploading I get no errors and the file thumbnail shows a PDF logo. When I go to place the image using [[File:testpdf.pdf]], it displays the clickable text File:testpdf.pdf, no rendered image.
I am also getting "0 × 0 pixels, file size: 1.37 MB, MIME type:" upon upload after further investigation. I went to edit php.ini as said in https://www.mediawiki.org/wiki/Extension:PdfHandler but that text does not exist.
In 1.26.3 it is still present!
pdfinfo has changed its behavior, so trying to read image size in function retrieveMetaData() (in file Pdfhandler.image.php ) you don't get expected result while using parameter. -meta! Image size will be registered in database with 0 x 0 pixel and thumbnail/picture of pdf page won't be rendered.
It helps to comment out the two lines in this function with "-meta". and " -l 999999" or at least parameter "meta" (losing some metadata").
Could be solved by refactoring different information requests in separate function calls with differnt parameters!
Using which pdfinfo and what version of it (There are multiple forks of the pdfinfo utility).
This is clearly not the case in general for all versions of pdfinfo, since it totally works fine on wikipedia and friends.
Err, the flow post had the actual useful information.
New versions of poppler pdfinfo changed how -meta worked https://bugs.freedesktop.org/show_bug.cgi?id=96801 - https://cgit.freedesktop.org/poppler/poppler/commit/utils/pdfinfo.cc?id=c91483aceb1b640771f572cb3df9ad707e5cad0d
So this is indeed a bug in PDFHandler.