What I was really looking to make, however, was a rectangular, not square, pocket, part of our planned design for my stepdaughter's wedding invitations. Not being able to find any instructions online or in books for rectangular pockets, I decided it was time to create a design for one. I quickly discovered it was not as easy as making the square. But where there's a will there's a way, and I had the will, so I found the way. Although I did take a bit of trial and error.
And this pocket envelope is easy to make. The difference is that there are more steps to make the rectangle than the square. And probably best to practice making one or two first. But overall I am very pleased with the result.
So, in case you wish to try making one too, here is a PDF with the instructions and a template. The measurements I've included are for a pocket envelope 6-1/2" wide and 5" high, which will fit quite neatly into a standard greeting card envelope.
PDF for Origami Pocket Envelope - Instructions for Rectangular Envelope
For a link to online instructions for square pocket envelope, click here.