Since the release of the latest update Bookends is able to set deep links:
“Introducing deep PDF links
You can create a hypertext link to any PDF text or annotation and insert in into 3rd party applications”
In DT it’s possible to set links to individual PDF pages, but not individual lines of text. Any chance, that this will be possible in the near future?
We don’t comment on development timeframes so we can’t say near. Future? Possibly but nothing concrete planned at this time.
Perhaps Bookends is a template, how to implement such a feature. 
I’m curious about what it would mean, in practical terms, to link to a line of text in a PDF file. All the PDF viewers I’ve ever seen are page-oriented, so a link to a line of text on a page would be equivalent to linking to the page – the viewer simply can’t behave differently except to display the page. Will Bookends behave differently somehow?
(I’m not necessarily dissing the idea, just trying to understand it better.)
Here is a short gif to show the way Bookend’s deep links works. (not shown in the gif) You highlight/mark a line of text, then right click and “copy link”. This link is copied into another app. (shown in the gif) If you click the link Bookends comes to the front with the right PDF opened, the right page and the right line of text highlighted and at the beginning of the window.
The next release will add additional parameters for item link URLs (and also the necessary contextual menu items to easily create them), meaning that this will be possible soon.
From the Bookends website: Bookends — Version History
• Introducing deep PDF links
You can create a hypertext link to any PDF text or annotation and insert in into 3rd party applications like Scrivener, DevonTHINK, and Obsidian, or into Bookends reference fields themselves (e.g. Notes). Deep links to selected text are created in the annotation popover window (Copy Link). You can create links to annotations in two ways: (1) right click on the annotation, select Copy Link from the contextual menu, and paste it into a compatible app, or (2) Command-drag the annotation to a window in a compatible app. Annotation links work with Highlight, Underline, Note, and Comment annotations created in Bookends or any other PDFKit-compliant application. If the corresponding Bookends library is open when the link is clicked, you will be taken to the reference/PDF and the linked text or annotation selected. In the copy or drag Bookends will also include a markdown link in the form[descriptive text](link). This allows you to use links with apps such as Obsidian and Bear, which do not recognize native links. You can rename the PDF without breaking the link. However, if you move a linked PDF Note or Comment on the page Bookends won’t be able to locate it. In this case Bookends will still open the PDF of the linked reference and take you to the correct page, it just won’t select the annotation. Note that to paste a live link into a reference field, it must support styled text and you must perform a plain Paste, not Paste And Match Style. If you set Command-V to use Paste And Match Style in Preferences, paste the link with Edit → Paste or the keyboard shortcut Shift-Option-Command-V.
Now it’s there. Thank you guys. Perfect service. #update