I am creating file sharing site so I need to get permissions from developer to share there software on my site. My question is that instead of uploading file to my server I can link to the developer site's download link not the download page as in this website freewareupdate.com. When I tried to download I got link from developer's site and this site has adsense enabled. Is getting permission that necessary as no one gonna know if I have them or not and Google too. Also if a keep my site name similar to filehorse or filehippo like filewhatever will it effect adsense approval?
no, you can make a similar site like that you just have to ensure that you do NOT offer i'llegal downloads without permission from author, trialware or linking to direct publisher sites are ok.
Read "Will providing software download or serial number be considered as copyright violation?" part from following link; https://support.google.com/adsense/answer/3394713?hl=en
Pirate software, warez, etc. You can't offer serial numbers, cracks, etc. Even if it is freeware or similar, you should read the licence and ask permission (if the licence doesn't answer your question) as the author might not want their work redistributed that way. You can link to the home page of legal software. You might want to consider offering the facility for the author to "claim" their entry so that they can update/remove it altogether or whatever they want to do.
Can I link directly to the download sever instead of linking to developers site as many sites do that as well? Like- instead of https://www.google.com/intl/en/chrome/browser/ I CAN USE http://dl.google.com/chrome/win/987E278CB......... ? Is taking permissions from them is that necessary for adsense approval as if take or not they won't be able to know that. Also what kind of software to avoid like youtube downloader etc.? Software description should be written by self or can be copied? Using screenshot or images from their website is okay or need to take that on my own?
I think you need to do more independent research using Google. There is a wealth of information out there. Regarding permission - imagine if Adsense sent you an email saying ads will be disabled for the site (not necessarily banning you) due to some software you host, then you could respond with evidence from the developer to show you have permission (as an example). You need to start being smarter and less lazy. Follow the licence (or developer instructions) about how to link.