MacOS – Set Preview to open PDFs in Thumbnail View by default on El Capitan

In Mountain Lion, at least, there's a Opening for the first time entry in the PDF pane in Preferences, where you can select Single Page. This sets the default view mode for all PDF files.

If you for some reason can't get it to work, you could try this Terminal command (don't know if it will work in Lion) and restart Preview:

defaults write -app preview kPVPDFDefaultPageViewModeOption -int 1

(in ML, the value of kPVPDFDefaultPageViewModeOption changes to 1 in Preview's plist, when selecting Single Page)

This is not a "permanent" change, but it speeds up the inconvenience of needing to use the "Tools" menu, by adding a keyboard shortcut:

Here is the first option for something you can do:

CREATING A KEYBOARD SHORTCUT

1. Open System Preferences
2. Click "Keyboard"
3. Open the tab titled "Shortcuts"
4. Scroll down to the last item on the left-hand frame's list: "App Shortcuts"
5. Click on the "plus sign" [+]; a smaller window will pop-up, asking for three lines of information:

— Select "Preview" for the application

– For "Menu Title", you must type EXACTLY what appears in the "Tools" menu of Preview: for OS El Capitan (Mac OS 10.11), this is currently "Rectangular Selection" (don't include quotation marks)

— For "Keyboard Shortcut", use whatever combination you want, so long as it does not conflict with any other pre-existing or currently used shortcuts. As an arbitrary example, I use "Command+Shift+R". Invent whatever alternative you might like.

6. Just a SIDE-NOTE: if you repeatedly press your keyboard shortcut [which you define in step 5], I have found that Preview will switch back to the "Text Selection" tool [when it is available], which might be occasionally [rarely!] convenient... since, (like you), I too wish that Rectangular Selection were the default... (especially for cropping, etc.)

Here is a second option, involving a "built-in" keyboard shortcut, combined along with one mouse-click [instead of the two required if using the "Tools" menu]:

1. Press "Command+Shift+A" to make the sub-toolbar, "Markup Toolbar" appear or disappear; [note: this toolbar has the rectangular selection option on the left].

2. With sub-toolbar available [see step 1], click the 2nd item in from the left, to enable rectangular selection.

Hope that helps!...

Note that, for some reason, I have not always had success with the 1st Option [programming an app-specific shortcut using System Preferences] in certain versions of Mac OS or with particular apps -- even though the menu item might be spelled precisely and correctly as it appears. It was thus pleasantly surprising to find that this custom keyboard-shortcut option indeed works under El Capitan [OS 10.11], as of the time of writing this here.

Hope this helps others!