I'm looking for softwares to manage my customers: able to search customers base on names, address, phone. save docs for each customer folder prepare contract for customer

Hi trung1987,

As long as the relevant details are entered on the customer's information, you can use the customer search function in QuickBooks Online to search by name, address or phone number:
 

1. Go to the Sales tab, then select Customers.
2. Begin typing in the Search field above the customer list. As you type, the matching customer(s) will appear in a dropdown menu to choose from. 

You can also save documents as attachments to your customer information:

1. Go to the Sales tab, then select Customers.
2. Click the customer's name. Then select the Edit option (look to the top right of the page).
3. Select the tab Attachments and upload your documents here, then Save.

If you are looking more for an app that will integrate with QuickBooks Online to help you manage your customers, you can check out the App Store for options. While these are third parties and we are unable to provide recommendations, each app has FAQs, customer reviews and so on so you can see what other QuickBooks users have experienced and recommend. 

-Kass

@trung1987 

Consider having a CRM app to integrate with your QBO. You may start exploring from these apps

https://freshsales.grsm.io/quickbooks

https://youdontneedacrm.com/?fpr=fiat34

https://fiatlux.teamwork.com/

Hope it helps.