I am a Postmaster and if your post office clerk is telling you that you can only ship documents in the flat rate envelopes then I would ask to talk with the Postmaster. There is no such rule. As long as your envelope can seal on its own before you tape it then it costs the flat rate of 4.95. It can be lumpy, lopsided, whatever, as long as you can close it properly and you didn't open the sides of the envelope to make it bigger. If you don't get satisfaction from the postmaster, then go to USPS.com and file a complaint and ask for it to be excalated to consumer affairs since you already spoke to the postmaster. The new padded envelopes are available on the webside also. Sorry for your bad experience, you shouldn't be treated that way.