You can, go to File > Place and navigate to PDF file, click on it then click Place button.
You can't change a PSD file into an INDD file because the INDD format isn't an image format - they're text files. To incorporate the image into the InDesign project, you have to perform a Place (File - Place) to put the image into the ID project. The image file then becomes a part of the overall ID file when it's saved, but it isn't changed to the ID format. InDesign links to the image file for both project presentation and printing purposes.
PSD files are Adobe Photoshop Document files. PSD files can be opened and edited with Adobe Photoshop, Adobe Photoshop Elements, and will also work with Corel's Paintshop Pro tool.
There are numerous of sites that offers free PSD files. Always read terms of use before downloading and using free PSD files. See related link for list of sites with free PSD files.
Yes, .psd files maintain the layers you create in Photoshop so that the next time you open your .psd file in Photoshop you can continue to work directly onto the layers.
If any program can save as PSD then this option is listed in Save or Save As dialog. GIMP can save as PSD.
Photoshp Documents
PSD is native Photoshop Document.
With the help of Photoshop or you may try alternative variant below. Program opens/reads/views/repairs .psd files.
Save it as .psd
Photoshop files use the extension .psd in Mac OS X.
Besides Photoshop, GIMP can also open PSD ( Photoshop Document ) files.Photoshop Elements can open almost fully editable PSD file. Some options are not available in pse like grouping and layer comps, some layer style options and so on but you can still open PSD and work with it. Also many other programs can open PSD files but not fully editable: Adobe Photoshop Lightroom, Adobe Illustrator, Corel Draw and so on.I can advise you an alternative variant below.
Yes, Photoshop is backwards compatible, however, once you save the file in CS5 you will not be able to use it in CS4 anymore. You can use files saved in CS5 in almost any other version and any page layout program which supports psd files, here i mean to save as psd. When saving turn on Maximize PSD and PSB File Compatibility in Edit > Preferences > File Handling.