Paraformaldehyde is just the solid, polymerized form of formaldehyde. Once you dissolve paraformaldehyde in a fluid, it is formaldehyde. Formaldehyde is an acceptable fixative for electron microscopy, though not the optimal one - it depends on what you need to visualize. As mentioned above, glutaraldehyde is overall a better fixative for EM.

Dear sir, this depends on the practical effect you wish to obtain. 

If you want organic tissues fixation, you must take notice that formaldehyde is produces strong dehydration.

I might prefer Gluteraldehyde, for postmortem fixation of organic tissues.

Paraformaldehyde is just the solid, polymerized form of formaldehyde. Once you dissolve paraformaldehyde in a fluid, it is formaldehyde. Formaldehyde is an acceptable fixative for electron microscopy, though not the optimal one - it depends on what you need to visualize. As mentioned above, glutaraldehyde is overall a better fixative for EM.

(apologize for lengthiness)

Dear Duaa,

despite my foreposters have said "right things" I would like to reflect a bit more in detail what you MIGHT have intended to ask...(apologize if I am wrong with that assumption).

It has already been said that when paraformaldehyde powder is dissolved [ adequately in distilled water or afterwards by mixing with a suited buffer solution] the end product will be the same as the name "formaldehyde" implies (If one means formaldehyde solution...). It is also right that formaldehyde solution itself - during the fixation process - exerts a (+/- strong) dehydrating effect onto (organic) tissular specimens.

As to the assumption formaldehyde (FA) to be an acceptable fixative I agree with a lot of CAVEATS! It will depend on the task your EM-study is being done.

A mixture of FA AND GA (Glutaraldehyde) in an appropriate buffer solution (maintained isotonicity and pH-buffering!) usually is at least in my honest opinion a good starting point for "good fixation" of samples in EM (but that "chapter" consists of too much parameters to be discussed in full length. "Aldehyde's" (in general GA) as fixative in ultrastructure research and enzyme cytochemistry  have been reported by Sabatini,et al., 1963, cf. http://www.ncbi.nlm.nih.gov/pubmed/13975866 (Free PMC Article), a mixture / combination of "aldehydes" (FA-GA) has been "invented in the last century (e. g.   -fixative, see *) below, just to name two of these "dino's").

*) http://library.med.utah.edu/WebPath/HISTHTML/MANUALS/KARNOV.PDF (no warranty for correctness)

So, at this point I would like to stop with my experiences (if you have any questions left, please just request in detailed manner)....and want to end here with:

if your question was to find out whether you can use (commercial available/purchaseable) Formaldehyde solution (e. g. min.38% for Histology, depending on the brand /company you will purchase that stuff) then my answer would be:

i) it depends on the quality of your FA-Stock-solution (not knowing which [national/international] sources you [can] use in Jordan)

ii) it depends on the task you are faced with (e.g., either only classical EM-morphology or else, more sophisticated techniques?)

iii) remember that most concentrated, commercially available FA-solutions (e.g. min. 36% FA) contain a stabilisator (usually about 10% methanol) and an ion-catching system (dolomite powder, nowadays CaCO3) to bind formic acid which is generated in FA-solutions due to "aging" and intrinsic chemical reactions, if not .....

The making of proper hydrous FA-solution for (T)EM (or SEM) from PFA (powder) is done easy, reliable and reproducible and -since "fresh" FA best used for all kind of special tissue fixation tasks.

Usually such information is contained also in textbooks of Electron Microcopy/electron microscopic preparation / methods / techniques...which can be found very easily in a specialized library or - if not available there - via Googleing (e.g. for example: < fixative or fix* Electron microscop* aldehyde buffer* >

Best wishes  & regards, Wolfgang

 Sorry for my coming back: 

If you want to read something about the issue, please (in the accessed RG-platform) insert  and find several former questions and threads regarding the matter... (puristic approach with more results I guess would be: 

https://www.researchgate.net/search.Search.html?type=question&query=formaldehyde           AND afterwards 

https://www.researchgate.net/search.Search.html?type=question&query=paraformaldehyde

Good luck, Wolfgang