copy / paste upgrades
The ability to select an image or area of a PDF and copy as bitmap would be very useful. Currently you have to take a screenshot, paste into an editor like Photoshop, then select the part you want. Right-click and Copy Image is hit and miss as it isn't clear what image is being copied and it often turns out to not be the image under the cursor. It would be ideal if you could select a rectangle and take a snapshot of it, preferably with the option of full resolution of the underlying image.
Allow customizing toolbar via advanced settings (add more actions and remove / change order of existing actions)
Booklet Printing PDF
I often print some articles to read while I am away from my computer. Adobe Reader has an option for "Booklet" printing. This feature scales, arranges, and prints pages such that A4 page is converted to A5 size and printed on A4 landscape orientation. We can take the printed pages, fold them at the (landscape) center, and staple them, such that we get a small easy-to-carry booklet. Can we get this feature in SumatraPDF? It would be a great addition. Keep up the good work!
Better annotation support
The basics of annotation tools are already present, and they work really well! But compared to other pdf viewers, the tools are quite limited and not really user friendly.
A way to delete currently opened file
Via command Delete Currently Opened File which will close the file and delete it (move it to trash).
Add quicklook (system wide preview)
When in file explorer, pressing space bar would show a preview window for the selected file. A quick way to preview file.