I have a manuscript and intends to submit it for publishing by the end of December and at the same time, I want to submit the abstract to be presented in a conference next April is that ok?
Generally conferences, seminars and workshops intended to discuss knew things. After presenting in the conference you can publish as you wish. But, I think, there is no restriction, to present published paper, you are the author for the paper. We can incorporate any suggestions received from discussion.
Be sure if the conference paper will not be published and at the same time be indexed in Scopus. Otherwise, you can extract part from the journal paper to be submitted to conference and then change the title and rewrite the abstract, body of the conference ( literatures) so that it does not looks alike. Reexplain the results of the extracted parts only and the conclusions. By so doing, it will be OK in that manner.
If the conference you intends submitting the whole work will publish it, then no need to submitting it to another journal again , to avoid same title and contents coming out in two different journals. My view though.
It should be the other way round. Present the idea in a conference, harvest comments and suggestions and repackage in a better form to be sent to a journal
In my opinion, it is unethical to send the abstract of an already submitted paper to a conference.
In general, conferences are good avenues for reporting ongoing works. This gives the researcher an opportunity to disseminate new findings and to get valuable feedback from the audience. Such presentations are also useful for the preparation of the paper for later publication because the audience’s questions may probe weaknesses in the work or the researcher’s account of it, and shows where s/he needs to expand and explain.
It depends on the journal and conference - if both the conference and journal are from the same professional society, it might be allowed (but check before you try it). For example, ASME and AIAA allow this for some conferences, but it would not work in general. For example, if you want to present at an IEEE conference and submit to a Springer journal, you will have problems.
Since you already prepared a journal paper, I am sure you have already noticed some holes and further work opportunities on your project - so why not just write about another aspect of your project for the conference?
Please is wrong, you can only modify the abstract and the work, before sending out for any conference. That is whIle you will here conference organizer telling you to send extended version of your work, when it comes to journal publication. Please