I have a pdf file of size 266KB which I open with Photoshop, crop out the boundaries and save it back again. The new file size is 7.96MB!
Since all I did was a crop, I did not expect the file size to increase. How can I save the pdf file so that the file size does not blow up like this?
You didn’t actually edit or crop the PDF. What you did was rasterize the entire the PDF by importing it into Photoshop. You then cropped this new raster image and exported that as a new PDF. In other words, your two PDFs have entirely different contents. Since one is mostly vector information and the other is a full-resolution pixel image, it’s no surprise the new one is a lot larger.
Modify the PDF in Illustrator or Acrobat, not Photoshop, if you want to retain the vector information and small file size.