While the optimal choice for converting documents to PDFs as well as editing them would be Adobe Acrobat, there are other options available. If a file is a Microsoft Office document and it needs to be converted into PDF (grant applications for example), it can be done by going to File, Save as, then scrolling to PDF. This option is available in Microsoft Office versions 2010 and 2013. For the 2007 version a plugin is available as well. Files that are created in OpenOffice or LibreOffice also have the Save as PDF option available.

One alternative to Adobe Acrobat is Foxit Reader. This software is able to convert your document to PDF as well as annotate it. While there is no option to merge or split the document, Foxit Reader allows you to edit the document by adding text, signatures and notes. To convert a document to PDF, open it with Foxit Reader, then click Save as and scroll down to PDF. While Foxit Reader is a very good alternative for converting files into PDFs, pdfcreator is another alternative. Pdfcreator allows you to create PDFs as well, but the options to edit, merge the files is only available in either the Pro version or as a separate module.

If annotation is needed, the alternative programs usually include this option. Foxit Reader includes options to highlight, strike out, and add notes to the PDF document.  Although Adobe Reader also comes with the option to annotate documents, only the paid version (Acrobat Pro) allows you to create PDF files as well.  Although there are websites that will convert your documents into PDF, this is not advisable as many websites store your files for a certain amount of time before deleting them. Some websites also do not notify you of how they handle your files in their terms of services or private policies. 

Links

Foxit Reader:

http://www.foxitsoftware.com/Secure_PDF_Reader/

Microsoft Office 2007 PDF Plugin:

http://www.microsoft.com/en-us/download/details.aspx?id=9943

LibreOffice:

https://www.libreoffice.org/