Never send articles to many venues at the same time without informing all of the editors you've pitched to. It's best not to submit proposals to numerous sites at the same time, although this is often necessary for timeliness.
The reason why you should never do this is because each publication has its own unique audience that will respond differently to your message. By submitting the same article to several publications, you are limiting yourself to one source of traffic and publicity for your story.
It's important to understand that while pitching stories to media outlets is common practice for journalists, doing so without permission from your sources can have negative effects on your career.
For example, if you write an article for a publication that uses material from another source without attribution, then they have the right to refuse future coverage from you. Furthermore, their readers may view you as untrustworthy if you don't give credit where it is due.
So in summary, pitching stories to media outlets is common practice for journalists but it isn't recommended because it limits your source pool and could affect your career.
No, you cannot simultaneously submit the same work to multiple journals. This is referred to as simultaneous or contemporaneous submission and is deemed unethical. You can write to the editor of each publication, providing a brief synopsis of your research and asking whether they are interested in it. If they accept your work, then there will be no problem publishing it in several places.
The only exception to this rule is if one of the journals states in their guidelines that they will accept simultaneous submissions. If this is the case, then you should follow their instructions completely.
Simultaneous submissions are common when researchers want to publish in many journals at once. This is done by writing short summaries of the papers, called "proposals", and sending them out to different publishers. The editors decide which proposals they want to pursue and sometimes contact the authors with feedback on their manuscripts. These are called "open calls" because they are open to all researchers who meet their criteria.
Simultaneous submissions are useful because they allow researchers to quickly obtain opinions on their work from different journals. If one journal rejects the manuscript, then another may still be interested in it so the author can choose which response to follow up with.
However, there are some risks involved with using this approach.
No, you cannot submit several manuscripts to the same conference or publication. You must receive negative comments before submitting it to another location. You may even devise a backup plan by submitting pre-submission enquiries to many journals at the same time. But otherwise, yes, you should create a unique manuscript for each presentation or publication.
The only exception is if you are presenting results from related work that was not included in your main study. In this case, you can use the same abstract and key words for both presentations. The reviewers will be able to connect the papers if they review them together.
However, it is not recommended because the reviewing process is not guaranteed to be fair. If you do this, you risk being rejected by all but one of the venues you send to. This doesn't mean you shouldn't try it out, but you should be aware of the risks.