MacOS – Can you add up front size at Preview

Auto-opening a downloaded file from a browser is done on pretty much a browser-to-browser basis. Since you asked about Chrome, here's the relevant blurb from Google's Docs:

Automatically open certain types of files

If you want certain types of files to always open after they're done downloading, click the arrow next to the file button in the downloads bar and select Always open files of this type. To prevent potentially malicious files from automatically downloading to your computer, this option isn't available for executable filetypes, such as those with .exe, .dll, or .bat extensions (for Windows), and .dmg extensions (for Mac).

Personally, these features weren't visible when I tried it, but then I hardly use Chrome other than for the odd web site test.

I've not found a way to get Preview to search for characters like # or +, but Skim, an alternative PDF viewer (homepage here), is a good replacement/addition to Preview and is able to search more specifically.

I've tested it and found it was able to find C++ (without needing any quotes/special options) without bringing up all C results.

It was also able to search specifically for accented characters (like é or ö) — though requires such characters to be accented in the search to find them (i.e. you can't search for blah and expect it to match bläh, nor vice versa). In Preview, either search will return matches for both accented and unaccented characters.