I dunno since when, but upload of PDF images fails, this hurts especially on tex.SE. Could this be an effect of an updated /etc/ImageMagick-6/policy.xml on the imgur server? At least on my Ubuntu 18.04 LTS machine, this file was modified two weeks ago.

• Could it be because your file is larger than 2 MB? – Sonic the Anonymous Hedgehog Oct 11 '18 at 16:09
• @Sonic no, because PDF is not an image and the image uploader supports uploading only, well, images. – Shadow The Burning Wizard Oct 11 '18 at 20:59
• No, the PDF was pretty small. And no, PDFs are images as per this answer on tex.meta.SE (being automatically converted). Edit: Used to be images? – quazgar Oct 12 '18 at 7:21
• I was surprised to know that Imgur supported PDF (from your linked meta post on TeX)... however, it seems it has failed on SE since 2013 – Meta Andrew T. Oct 27 '18 at 17:34
• True, so it's probably a duplicate of that tex.meta question. – quazgar Nov 6 '18 at 10:37
• @quazgar no, PDF is not an image, no matter how you try to look at it. It can be converted to image, but that's not something SE can or should be doing. This is still not a bug in any way. – Shadow The Burning Wizard Feb 28 '19 at 9:51