Some PDf files have 'tooltip' feature on them. For an example document, see the section 3.2 (\pdftooltip command) of the 'package documentation' file on this website (https://www.ctan.org/pkg/pdfcomment). I tested this using the aformentioned .pdf file and various PDF readers. It worked perfectly with Microsoft Edge (Windows), SumatraPDF (Windows, Wine on Linux and macOS), Adobe Acrobat Reader (Windows and macOS), and Foxit reader (Windows, Linux, and macOS). But not with Evince. (Actually I couldn't find any Linux-native reader that support this tooltip feature.) An Evince developer told me that this is because Poppler doesn't support API for tooltips (https://bugzilla.gnome.org/show_bug.cgi?id=793986).
Please attach a file.
Created attachment 137770 [details] pdf file with a few tooltip annotations Extracted from the example file of the LaTeX 'pdfcomment' package.
Extracting one of the three annotations in the example file we get << /Type /Annot /Subtype /Widget /TU (Sulfuric\040acid) /T (tooltip zref@1) /C [ ] /FT/Btn /F 768 /Ff 65536 /H/N /BS << /W 0 >> /Rect [417.169 745.106 451.341 754.196] >> So it looks like a merged Field and Annot dictionary...Aren't fields supposed to belong to Forms? I don't find the /T entry anywhere, so I don't know that the (tooltip zref@1) means
No, AnnotWidgets can also be standalone, see } else if(!strcmp(typeName, "Widget")) { in Annot.cc but it's true we don't see to support Widgets that don't belong to Forms very well "(tooltip zref@1)" means nothing, what you're interested in is the TU field that which we're not parsing in AnnotWidget::initialize. Basically this "tooltip" is implemented as an invisible button, kind of a hack if you ask me, but yeah we should try to support them.
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