ولقد وقع اختيارنا على كابتن أحمد كمرشح ملائم للوظيفة وجاري الإنتهاء من إجراءات تعيينه

ولقد اختارنا كابتن أحمد كمرشح مناسب وجاري الإنتهاء من إجراءات تعيينه

Appointment: تعيين

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والله أعلم

وقمنا بتعيين/ عينا

English term (edited): placed... as a candidate

"Placed" is an empty verb in this context. Accordingly, I suggest the following:

رشحنا
OR
قمنا بترشيح
the second suggestion has an equal Arabic empty verb which is not advisable to use in general. However, we may use it at very minimal instances that allow for such a usage.

HTH

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Note added at 3 days 5 hrs (2019-12-18 14:00:34 GMT)
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In SFL grammar that takes looks into semantics and meaning making, there is a type of verbs that is described as a lexically empty verb. It means that "the process of the clause is expressed only by the noun functioning as Scope" [Halliday & Matthiessen, 2004: 139]

the verb "have" and "make" in "They have a walk. You make a call" are lexically empty verbs. We translate it as follows:
يتمشون
تتصل هاتفيًا

"Consider I play tennis, where tennis is Scope. The game of tennis is clearly not an entity; there is no such thing as tennis other than the act of playing it. Similarly with sing a song; if we look up song in the dictionary we are likely to find it defined as ‘act of singing’, just as
game is ‘act of playing’."[Halliday & Matthiessen, 2004: 139]

Please read this carefully the following excerpt to know why we use such lexically empty verbs:

"There are various reasons in English grammar why this has become a favoured construction. The main reason for its prevalence is the greater potential that is open to nouns, in contrast to verbs, for being modified in different ways: it would be hard to replace the nouns by verbs in examples such as have a hot bath, do a little dance, made three serious mistakes, take another quick look, gave her usual welcoming smile, made minor revisions.
Compare the example the jewellers hadn’t done the evaluation yet, where if the Scope is replaced by a process hadn’t valued, on the one hand this would require an explicit Goal, and on the other hand it could not be made specific with the." [Halliday & Matthiessen, 2004: 139]

وفي رأيي يمكننا الاستعاضة عن هذا الفعل باستخدام المفعول المطلق في أحيان كثيرة فيمكننا القول
ساروا سيرًا طويلًا
as an equivalent for "They had a long walk"

place so and so as a candidate
تعني ترشيحه والفعل هنا ليس له معنى دلالي وظيفي
وإن ترجمناه فستكون الترجمة
word for word

والله أعلى وأعلم


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Note added at 3 days 5 hrs (2019-12-18 14:03:21 GMT)
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**that looks into semantics and meaning making

نعين السيد احمد لمنصب