I did follow the link that you provided and read all the requirements listed on that particular web page. You didn't indicate what software you use to generate your documents, but I'll assume you use software such as Microsoft Word. Some thoughts:
(1) The actual stated requirements are not at all stringent and in fact give you quite a bit of flexibility. In fact, these are some of the most lenient “requirements” I've seen in a long time. It is quite easy to comply with them.
(2) Font point size. The size specified as minimum (11 point) matches the default of current versions of Microsoft Word. For the NIH recommended fonts, adhering to that 11 point setting will not violate the Type Density requirement. There is a comment in those guidelines that “some PDF conversion software reduces font size” – that is not the case with the PDFMaker conversion software for Microsoft Office that comes with Adobe Acrobat. Likewise, that is not a problem with any PDF generated by other Adobe layout software including FrameMaker and InDesign. In the case of serif fonts (such as the recommended Georgia or Palatino Linotype typefaces), you should seriously consider 12 point as your minimum for ease of reading.
(3) Line Spacing. Again, if you use the NIH recommended fonts in Microsoft Word or any standard layout software using at least the minimum font point size with single spacing by default you will not exceed the line spacing maximum of 6 lines of text per inch. Personally, I think that such density is too high. With Microsoft Word, I would set the line spacing for the paragraph as multiple 1.2 or no less than multiple 1.1 spacing. With advanced page layout software where you set exact leading values, you should use a default of either 1.2 (usually the program default) or at minimum 1.1x point size.
(4) Neither the page size nor the margin requirements are overly restrictive. Obviously, you will need to reformat to letter size (8.5x11) if your content is originating from the rest of the world for which the standard letter size page is A4 (narrower, but longer that US letter).
In terms of “applications that can support this,” virtually any word processor or layout software can support these requirements if you parameterize them properly and especially if you define templates and styles and adhere to same when creating and editing your documents.
Of course, the problem is different if what is happening is that you are receiving PDF files that you are submitting to NIH and that you want/need to quickly check for compliance with the NIH requirements. In this case, Acrobat Pro's Preflight is what you need. Using single check tests, Preflight can check for text smaller than a specified point size which in general would also pickup line spacing problems.
Hopefully, this begins to assist you. Let me know if you have more specific questions.
- Dov