What information about a filed technology patent and something which is highly confidential can be shared with a potential investor?

Easiest approach: If the potential investor signs a properly-drafted nondisclosure agreement, you can share everything.This answer is not a substitute for professional legal advice....

After a patent is filed, the patent office does not care how much of the application you are willing to disclose. So, it is all up to you. How much do you trust the investor? How badly do you need their support? How easy would be for someone to duplicate your method by simply reading the patent application? Note that the patent eventually will be published. You can also ask the investor to review the patent application under NDA, but you can offer to provide a less detailed review of your invention without NDA.

I agree with Lang McHardy, determine when your patent application will  publish and this issue may become moot.   If it will be published in the near future, you may well share everything.  Once it is published, it will no longer be confidential.  You can also get a non-disclosure agreement (as suggested by Konstantinos).  It's easy and cheap, although may be hard to enforce. It seems like a reasonable request by the investor to want to look at the patent application, since it sounds like the market value of your product heavily depend on the issued patent (i.e., having exclusive rights).  It also sounds like he does not yet fully understand the invention.  Without knowing the product it's hard to say, but is there another way to sufficiently educate him/her?  A meeting between the relevant parties to go over the concepts of the invention?  Thereby your patent claims remain confidential. On a side note, the investor cannot legally steal your idea and patent it as he/she is not the inventor, and your patent (assuming it is issued) will allow you to prevent others from producing the invention.  Of course, the investor could illegally steal the idea and try to market it.  But he/she could also do that once the patent application is published. In conclusion to my above chatter, the investor can eventually find out details about your patent application, it's just a matter of when and whether that time will make a difference.