At least as of the 3.06 version of TexShop (and perhaps earlier), TeXShop has included a Find Panel that uses OgreKit, which is a Cocoa framework. (It was developed by Isao Sonobe, according to the TeXShop help center.)
Basically, this means that this find panel ends up being much more powerful, in particular because it can utilize regular expressions. Additionally, this OgreKit version of the find panel allows one to set the scope of any given search. The two options for setting the scope are "Entire File" and "Selection".
In order to use the OgreKit version of the find panel, you need to open TeXShop, go to Preferences, and, under the Source tab in the Preferences, change the Find Panel radio option to "OgreKit Find Panel". After changing this, you will have to restart TeXShop, but you should then be able to set the scope of a search to the text that you have selected.
Update:
However, based on my testing this feature as of TeXShop version 3.18, this feature does not seem to work with find
. For example, if one selects a block of text and then uses only the find
function of the find panel, it will search the entire file. This is true for any function that does not include "all". That is, the only functions that really seem to work with this scope option are find all
and replace all
. I'm not sure why this is the case. Nonetheless, you should be able to at least use those two "all" functions with the scope restrictor as of version 3.18 of TeXShop. I've just reported this to Richard Koch; I'll update this answer accordingly.
Texmaker comes with a build in PDF previewer that supports synctex. If I remember correctly, it is "embedded" by default. That is, editor and previewer is a part of the same bigger window. This might not be useful if the screen is small, say on a small laptop. Editor and previewer can be separated into two separate Windows via the Texmaker configuration (just remove the tick mark at "embedded" and restart Texmaker)
Texmakers cousin Texstudio made this even easier: there the separation is a button on the previewer.
Best Answer
In section 2.4 (Working with a Large Document) of the "TEXShop tips & tricks" there are some clues for you.
This is has two benefits:
P.S. You can access to "TEXShop tips & tricks" from help menu.