In Evince, panning of a document with what works like the "hand" tool in "competitive" PDF viewers (Okular, qpdfviewer, Adobe Acrobat) is triggered with the middle mouse button (if you have one). To have the same feature with your touch pad, you need a way to emulate a middle click with your touchpad. That may require changing some configuration options for your touchpad if you cannot achieve that by default.
What options are exposed or are available will depend on your desktop environment, on the driver you use (e.g. synaptics or libinput) and on your touchpad hardware. Thus, how you can emulate a middle mouse click, or enable such emulation, will depend on these factors. How I solved it for myself therefore is provided only as first inspiration because it may be different in your case.
For me, Gnome Tweak Tool exposes two options for "Mouse click emulation", "Fingers" and "Area". Although "Fingers" is supposed to emulate a middle mouse click with three fingers, that does not work for me. "Area", however, works. I can press the middle of the bottom area, the cursor changes to a hand and I am in business.
Users that have two-finger scrolling or both horizontal and vertical edge scrolling probably will never have noticed the issue. Also here, one can quite conveniently pan across a zoomed document. Rather than dragging the canvas with the hand tool, here it is a matter of scrolling. I do not like "two-finger" scrolling, because it gives issues in a case where you have a text document with one or more landscape pages inserted. Then, any scrolling with two fingers likely will also shift your document to the left or to the right (unless you very carefully make sure to have a strictly vertical two-finger movement, that is).
Yet, this lack of discoverability and dependency of the hardware of the user and the configuration (what if the mouse does not have a scrolling wheel?) is an issue with Evince.
