i want windw app in c#for converting imgs to searchable pdf

To generate a searchable PDF from images, you need to use a toolkit that has Optical character recognition features and supports saving document PDF. Check the following example that uses leadtools to OCR scanned images and convert them into text files.
http://support.leadtools.com/CS/forums/43549/ShowPost.aspx
You can modify the code so it can save the resulting text as searchable PDF.

Here is a sample project on MSDN that converts image to PDF in .NET platform using a free PDF library -

http://code.msdn.microsoft.com/How-to-Convert-Image-to-da2dfd65

Reference the dll to you own project, then you can use the sample code to make the conversion from image to PDF.Hope this is helpful.