Sending your paper around in Economics As a PhD student I made a few connections over the course of time with professors from around Europe (had brief chats with them at conferences, invited them at conferences, etc..). Some explicitly said, send me your paper once it is ready, other haven't.

Is it common in Economics to send your paper, without an explicit invitation, asking for feedback (assuming the speaker to be in the relevant field)? Or should one wait or look for a chance to present it in a seminar?
Is it common in Economics to send your paper, without an explicit invitation, asking for feedback (assuming the speaker to be in the relevant field)?

I am not sure this is common in Econ but I have definitely done it! Note that you increase the probability of getting feedback if 


you know or met the author, 
he/she asked you to send your paper,
you cite their work.


Or should one wait or look for a chance to present it in a seminar?

This is probably your best chance to get feedback given that profs are very busy. A bunch of universities and associations organize PhD seminars, workshops, conferences or poster sessions. Look at inomics. You may also contact profs with the intention to present your work in their seminars.